Additives for property modification in ceramic composite bodies

ABSTRACT

This invention relates generally to a novel method of manufacturing a composite body. More particularly, the present invention relates to a method for modifying the resultant properties of a composite body, by, for example, minimizing the amount of porosity present in the composite body. Moreover, additives, whether used alone or in combination, (1) can be admixed with the permeable mass, (2) can be mixed or alloyed with the parent metal, (3) can be placed at an interface between the parent metal and the preform or mass of filler material, (4) or any combination of the aforementioned methods, to modify properties of the resultant composite body. Particularly, additives such as VC, NbC, WC, W 2  B 5 , TaC, ZrC, ZrB 2 , SiB 6 , SiC, MgO, Al 2  O 3 , ZrO 2 , CeO 2 , Y 2  O 3 , La 2  O 3 , MgAl 2  O 4 , HfO 2 , ZrSiO 4 , Yb 2  O 3  and Mo 2  B 5  can be combined with the permeable mass in an amount of about 5-50 percent by weight, prior to reactively infiltrating the permeable mass. Moreover, an additive may also include substantially pure elemental metals (e.g., Nb, Ti, Hf, V, Ta, Cr, Mo, Al, Cr, Si, Co and W) which may be provided by any of the methods discussed above herein.

This application is a continuation-in-part of U.S. application Ser. No.07/551,903, now abandoned, filed Jul. 12, 1990, in the names of TerryDennis Claar et al., which is a continuation-in-part of application Ser.No. 07/282, 462, now abandoned, filed Dec. 9, 1988, in the names ofTerry Dennis Claar et al., which is a continuation-in-part ofapplication Ser. No. 07/137,397, now abandoned, filed Dec. 23, 1987, inthe names of Terry Dennis Claar et al., and all of which are entitled "AMethod of Producing and Modifying the Properties of Ceramic CompositeBodies." The subject matter of each of the above-identified applicationsis hereby expressly incorporated by reference.

TECHNICAL FIELD

This invention relates generally to a novel method of manufacturing aceramic composite body, for example, a ZrB₂ -ZrC-Zr composite body(hereinafter referred to as "ZBC" composite body). More particularly thepresent invention relates to a method for modifying the resultantproperties of a ceramic composite body, by, for example, minimizing theamount of porosity present in the composite body. The composite bodycomprises one or more boron-containing compounds (e.g., a boride or aboride and a carbide) which has been made by the reactive infiltrationof a molten parent metal into a bed or mass containing boron carbide, anadditive material, and optionally one or more inert fillers, to form thecomposite body. Particular emphasis is placed upon modifying theproperties of a ZBC composite body (e.g., reactively infiltrating a masscontaining boron carbide with a zirconium parent metal). However, themethods disclosed herein are believed to be generic to a number ofdifferent parent metals.

BACKGROUND ART

In recent years, there has been an increasing interest in the use ofceramics for structural applications historically served by metals. Theimpetus for this interest has been the relative superiority of ceramics,when compared to metals, with respect to certain properties, such ascorrosion resistance, hardness, wear resistance, modulus of elasticityand refractory capabilities.

However, a major limitation on the use of ceramics for such purposes isthe feasibility and cost of producing the desired ceramic structures.For example, the production of ceramic boride bodies by the methods ofhot pressing, reaction sintering, and reaction hot pressing is wellkhown. While there has been some limited success in producing ceramicboride bodies according to the above-discussed methods, there is still aneed for a more effective and economical method to prepare denseboride-containing materials.

In addition, a second major limitation on the use of ceramics forstructural applications is that ceramics generally exhibit a lack oftoughness (i.e., damage tolerance, or resistance to fracture). Such lackof toughness tends to result in sudden, easily induced, catastrophicfailure of ceramics in applications involving rather moderate tensilestresses. This lack of toughness tends to be particularly common inmonolithic ceramic boride bodies.

One approach to overcome the above-discussed problem has been theattempt to use ceramics in combination with metals, for example, ascermets or metal matrix composites. The objective of this known approachis to obtain a combination of the best properties of the ceramic (e.g.,hardness and/or stiffness) and the best properties of the metal (e.g.,ductility). While there has been some general success in the cermet areain the production of boride compounds, there still remains a need formore effective and economical methods to prepare dense boride-containingmaterials.

DESCRIPTION OF COMMONLY OWNED U.S. PATENTS AND PATENT APPLICATIONS

Many of the above-discussed problems associated with the production ofboride-containing materials have been addressed in commonly owned andco-pending U.S. patent application Ser. No. 07/551,306, filed on Jul.12, 1990, in the names of Terry Dennis Claar et al, which is acontinuation-in-part of U.S. patent application Ser. No. 07/446,433,filed on Dec. 5, 1989, in the names of Terry Dennis Claar et al., as acontinuation of commonly owned U.S. patent application Ser. No.07/296,771, which issued on Dec. 5, 1989, as U.S. Pat. No. 4,885,130.U.S. patent application Ser. No. 07/296,771, was a continuation-in-partof U.S. patent application Ser. No. 07/137,044, filed on Dec. 23, 1987,and now allowed, in the names of Terry Dennis Claar et al., which was acontinuation-in-part of U.S. patent application Ser. No. 07/073,533,filed in the names of Danny R. White, Michael K. Aghajanian and T.Dennis Claar, on Jul. 15, 1987, and entitled "Process for PreparingSelf-Supporting Bodies and Products Made Thereby". The above-discussedseries of applications and Patent are hereinafter sometimes referred toas "the '433 Series".

Briefly summarizing the disclosure of the '433 Series, self-supportingceramic bodies are produced by utilizing a parent metal infiltration andreaction process (i.e., reactive infiltration) in the presence of a (1)boron carbide or (2) boron carbide and at least one of a boron donormaterial and/or a carbon donor material or (3) a boron donor materialand a carbon donor material. Particularly, for example, a bed or mass ofboron carbide is infiltrated by molten parent metal, and the bed may becomprised entirely of boron carbide, thus resulting in a self-supportingbody comprising one or more parent metal boron-containing compounds,which compounds include a parent metal boride or a parent metal borocarbide, or both, and typically also may include a parent metal carbide.It is also disclosed that, for example, the mass of boron carbide whichis to be infiltrated may also contain one or more inert fillers mixedwith the boron carbide. Accordingly, by combining an inert filler, theresult will be a composite body having a matrix produced by the reactiveinfiltration of the parent metal, said matrix comprising at least oneboron-containing compound, and the matrix may also include a parentmetal carbide, the matrix embedding the inert filler. It is furthernoted that the final composite body product in either of theabove-discussed embodiments (i.e., filler or no filler) may include aresidual metal as at least one metallic constituent of the originalparent metal.

Broadly, in the disclosed method of the '433 Series, a mass comprising,for example, boron carbide is placed adjacent to or in contact with abody of molten metal or metal alloy, which is melted in a substantiallyinert environment within a particular temperature envelope. The moltenmetal infiltrates the boron carbide mass and reacts with at least theboron carbide to form at least one reaction product. The boron carbideis reducible, at least in part, by the molten parent metal, therebyforming the parent metal boron-containing compound (e.g., a parent metalboride and/or boro compound under the temperature conditions of theprocess). Typically, a parent metal carbide is also produced, and incertain cases, a parent metal boro carbide is produced. At least aportion of the reaction product is maintained in contact with the metal,and molten metal is drawn or transported toward the unreacted boroncarbide by a wicking or a capillary action. This transported metal formsadditional parent metal boride, carbide, and/or boro carbide and theformation or development of a ceramic body is continued until either theparent metal or boron carbide has been consumed, or until the reactiontemperature is altered to be outside of the reaction temperatureenvelope. The resulting structure comprises one or more of a parentmetal boride, a parent metal boro compound, a parent metal carbide, ametal (which, as discussed in the '433 Series, is intended to includealloys and intermetallics), or voids, or any combination thereof.Moreover, these several phases may or may not be interconnected in oneor more dimensions throughout the body. The final volume fractions ofthe boron-containing compounds (i.e., boride and boron compounds),carbon-containing compounds, and metallic phases, and the degree ofinterconnectivity, can be controlled by changing one or more conditions,such as, for example, the initial density of the boron carbide body, theamount of boron donor material and/or carbon donor material relative toboron carbide and parent metalathe relative amounts of boron carbide andparent metal, alloys of the parent metal, dilution of the boron carbidewith a filler, temperature, and time, etc. Preferably, conversion of theboron carbide and/or boron donor material and/or carbon donor materialto the parent metal boride, parent metal boro compound(s) and parentmetal carbide is at least about 50%, and most preferably at least about90%.

The typical environment or atmosphere which was utilized in the '433Series was one which is relatively inert or unreactive under the processconditions. Particularly, it was disclosed that an argon gas, or avacuum, for example, would be suitable process atmospheres. Stillfurther, it was disclosed that when zirconium was used as the parentmetal, the resulting composite comprised zirconium diboride, zirconiumcarbide, and residual zirconium metal. It was also disclosed that whenaluminum parent metal was used with the process, the result was analuminum boro carbide such as Al₃ B₄₈ C₂, AlB₁₂ C₂ and/or AlB₂₄ C₄, withaluminum parent metal and other unreacted unoxidized constituents of theparent metal remaining. Other parent metals which were disclosed asbeing suitable for use with the processing conditions included silicon,titanium, hafnium, lanthanum, iron, calcium, vanadium, niobium,magnesium, and beryllium.

Still further, it is disclosed that by adding a carbon donor material(e.g., graphite powder or carbon black) and/or a boron donor material(e.g., a boron powder, silicon borides, nickel borides and iron borides)to the mass comprising boron carbide, the ratio of parentmetal-boride/parent metal-carbide can be adjusted. For example, ifzirconium is used as the parent metal, the ratio of ZrB₂ /ZrC can bereduced if a carbon donor material is utilized (i.e., more ZrC isproduced due to the addition of a carbon donor material in the mass ofboron carbide) while if a boron donor material is utilized, the ratio ofZrB₂ /ZrC can be increased (i.e., more ZrB₂ is produced due to theaddition of a boron donor material in the mass of boron carbide). Stillfurther, the relative size of ZrB₂ platelets which are formed in thebody may be larger than platelets that are formed by a similar processwithout the use of a boron donor material. Thus, the addition of acarbon donor material and/or a boron donor material may also affect themorphology of the resultant material.

U.S. Pat. No. 4,885,131 (hereinafter "Patent '131"), issued in the nameof Marc S. Newkirk on Dec. 5, 1989, and entitled "Process For PreparingSelf-Supporting Bodies and Products Produced Thereby", disclosesadditional reactive infiltration formation techniques. Specifically,Patent '131 discloses that self-supporting bodies can be produced by areactive infiltration of a parent metal into a mixture of a bed or masscomprising a boron donor material and a carbon donor material. Therelative amounts of reactants and process conditions may be altered orcontrolled to yield a body containing varying volume percents ofceramic, metals, ratios of one ceramic or another and porosity. Themethods of Patent '131 were improved upon by copending U.S. applicationSer. No. 07/551,747, filed on Jul. 12, 1990, in the names of Marc S.Newkirk et al., which was a continuation-in-part of U.S. Pat. No.5,010,044, which issued on Apr. 23, 1991, in the name of Marc S.Newkirk, which was a continuation of Patent '131.

In another related patent application, specifically, copending U.S.patent application Ser. No. 07/551,486, filed on Jul. 12, 1990, in thenames of Terry Dennis Cla ar et al., which is a continuation-in-part ofU.S. patent application Ser. No. 07/296,770 (hereinafter referred to as"Application '770"), filed in the names of Terry Dennis Claar et al., onJan. 13, 1989, and entitled "A Method of Producing Ceramic CompositeBodies", additional reactive infiltration formation techniques aredisclosed. The above-discussed series of applications are hereinaftersometimes referred to as "the '486 Series". Specifically, the '486Series discloses various techniques for shaping a bed or mass comprisingboron carbide into a predetermined shape and thereafter reactivelyinfiltrating the bed or mass comprising boron carbide to form aself-supporting body of a desired size and shape.

U.S. Pat. No. 5,011,063 (hereinafter "Patent '063") which issued on Apr.30, 1991, in the name of Terry Dennis Claar, and entitled "A Method ofBonding A Ceramic Composite Body to a Second Body and Articles ProducedThereby", discloses various bonding techniques for bondingself-supporting bodies to second materials. Particularly, this Patentdiscloses that a bed or mass comprising one or more boron-containingcompounds is reactively infiltrated by a molten parent metal to producea self-supporting body. Moreover, residual or excess metal, is permittedto remain bonded to the formed self-supporting body. The excess metal isutilized to form a bond between the formed self-supporting body andanother body (e.g., a metal body or a ceramic body of any particularsize or shape). The methods of Patent '063 were improved upon bycopending and related U.S. application Ser. No. 07/551,290, filed onJul. 12, 1990, in the name of Terry Dennis Claar.

The reactive infiltration of a parent metal into a bed or masscomprising boron nitride is disclosed in U.S. Pat. No. 4,904,446(hereinafter "Patent '446"), issued in the names of Danny Ray White etal., on Feb. 27, 1990, and entitled "Process for PreparingSelf-Supporting Bodies and Products Made Thereby". Specifically, thispatent discloses that a bed or mass comprising boron nitride can bereactively infiltrated by a parent metal. A relative amount of reactantsand process conditions may be altered or controlled to yield a bodycontaining varying volume percents of ceramic, metal and/or porosity.Additionally, the self-supporting body which results comprises aboron-containing compound, a nitrogen-containing compound and,optionally, a metal. Additionally, inert fillers may be included in theformed self-supporting body.

A further post-treatment process for modifying the properties ofproduced ceramic composite bodies is disclosed in copending U.S. patentapplication Ser. No. 07/296,966 (hereinafter "Application '966"), filedin the names of Terry Dennis Claar et al., on Jan. 13, 1989, andentitled "A Method of Modifying Ceramic Composite Bodies ByPost-Treatment Process and Articles Produced Thereby". Specifically,Application '966 discloses that self-supporting bodies produced by areactive infiltration technique can be post-treated by exposing theformed bodies to one or more metals and heating the exposed bodies tomodify at least one property of the previously formed composite body.One specific example of a post-treatment modification step includesexposing a formed body to a siliconizing environment.

U.S. Pat. No. 5,019,539 (hereinafter "Patent '539"), which issued in thenames of Terry Dennis Claar et al., on May 28, 1991, and entitled "AProcess for Preparing Self-Supporting Bodies Having Controlled Porosityand Graded Properties and Products Produced Thereby", discloses reactinga mixture of powdered parent metal with a bed or mass comprising boroncarbide and, optionally, one or more inert fillers. Additionally, it isdisclosed that both a powdered parent metal and a body or pool of moltenparent metal can be induced to react with a bed or mass comprising boroncarbide. The body which is produced is a body which has controlled orgraded properties.

The disclosures of each of the above-discussed Commonly Owned U.S.Patent Applications and Patents are herein expressly incorporated byreference.

SUMMARY OF THE INVENTION

The present invention has been developed in view of the foregoing and toovercome the deficiencies of the prior art.

One aspect of the invention provides a method for controlling orreducing the amount of porosity present in a composite body. Moreparticularly, the amount of porosity can be reduced by utilizing atleast one of two different methods, taken alone or in combination. Thefirst method relates to admixing an additive material comprising atleast one of tantalum carbide, zirconium carbide, and/or zirconiumdiboride with a permeable mass of reactant material (e.g., boroncarbide), prior to reactively infiltrating the mass with a parent metal.The second method utilizes a particular zirconium parent metal (e.g., azirconium sponge) as the parent metal for forming a composite body. Byreducing the amount of porosity in these composite bodies, the machiningrequired to remove undesirable porosity can be reduced, if notcompletely eliminated.

Broadly, in accordance with a first feature of the invention, anadditive material comprising at least one of tantalum carbide (TaC),zirconium carbide (ZrC), silicon carbide (SiC) and/or zirconium diboride(ZrB₂) can be admixed with a boron and/or carbon containing material(e.g., B₄ C) to form a permeable mass which is to be reactivelyinfiltrated. Further, an additive material may comprise at least one ofthe following refractory oxides or borides: alumina (Al₂ O₃), magnesia(MgO), spinel (e.g., MgAl₂ O₄), yttria (Y₂ O₃), lanthanum oxide (La₂O₃), calcium oxide (CaO), hafnium oxide (HfO₂), borides of silicon(e.g., SiB₆, SiB₄), zirconium oxide (ZrO₂), cerium oxide (CeO₂),ytterbium oxide (Yb₂ O₃), zircon (ZrSiO₄) etc. The above-discussedadditive materials can be added in an amount of about 5-50 percent byweight. After admixing the raw materials together, the same can beformed into a preform, in accordance with, for example, the disclosurein the '433 Series.

Still further, in accordance with a second feature of the invention, azirconium metal sponge containing less than 1000 ppm by weight tin,preferably less than 500 ppm by weight tin, as an alloyed contaminant,can be utilized as a parent metal instead of the parent metal disclosedin the '433 Series, which contained about 1000-2000 ppm, by weight, tin.By utilizing either of the above-broadly disclosed methods, a compositebody having a reduced amount of porosity can be formed.

In addition, other additive materials, alone or in combination, (1) canbe admixed with the boron and/or carbon containing material (e.g., boroncarbide), (2) can be mixed or alloyed with the parent metal, (3) can beplaced at an interface between the parent metal and the preform or massof filler material (e.g., a preform comprising boron carbide, a fillermaterial and an additive material), or (4) and combination of theaforementioned methods, to modify the properties of the resultantcomposite body. Particularly, additive materials such as VC, NbC, WC, W₂B₅ and Mo₂ B₅ can be combined with the B₄ C material in an amount ofabout 5-50 percent by weight, prior to reactively infiltrating the B₄ Cmaterial. These additive materials, as well as those discussed above(i.e., CeO₂, TaC, ZrC and ZrB₂), may affect such properties as hardness,modulus of elasticity, density and grain size. Further, additivematerials may comprise refractory oxides such as (CeO₂, MgO, ZrO₂, Y₂O₃, stabilized ZrO₂, etc.) which may be admixed with the permeable massto be reactively infiltrated in order to, for example, enhance thecreep-resistance of the formed composite body.

Moreover, depending upon the process conditions (e.g., temperature) andthe particular reactive infiltration system (i.e., combination of parentmetal, permeable mass, atmosphere, etc.) selected an additive materialmay also include substantially pure elemental metals and alloys (e.g.,aluminum, silicon, chromium, titanium, niobium, nickel, cobalt, etc.,which may be provided by any of the methods discussed above herein).Further, a metal such as titanium can serve as both a parent metal andan additive material. Typically, the relative quantity of a particularmetal may determine which metal functions primarily as the parent metal(e.g., a metal having the greater quantity tends to correspond to aparent metal as defined above herein). However, at least a portion of anadditive material comprising a metal may also react with the permeablemass of material to form an additive metal carbide and/or additive metalboride , etc. More importantly, the preference of a parent metal versusan additive material to react with the permeable mass being reactivelyinfiltrated is dependent upon a number of factors including the relativereactivities of the respective metals with the constituents of thepermeable mass under the process conditions selected (e.g., when analloy comprising zirconium and chromium is reactively infiltrated into apermeable mass comprising boron carbide, the zirconium constituent ofthe alloy typically has a greater affinity or is more reactive with theboron carbide than the chromium or additive material constituent).Further, it has been observed that a zirconium alloy containing fromabout 0.5 to about 10 weight percent of an additive metal comprisingniobium, preferably, about 1-5 weight percent niobium, can produce aself-supporting body which displays a reduction in grain size relativeto a body produced without any significant amounts of niobium beingpresent. Particularly, the additive metal (e.g., niobium, titanium,etc.) may be present in the ceramic and/or metallic phases of the formedcomposite. Therefore, the presence of additive metals comprisingaluminum, silicon, chromium, niobium, etc., in a formed self-supportingbody may result in a body which has superior mechanical, physical andthermal properties (e.g., enhanced high temperature strength, oxidationresistance, corrosion resistance, etc. Moreover, additive metalscomprising nickel, cobalt, and alloys thereof may provide enhanced creepresistance properties to the formed composite body relative to similarlyproduced bodies which do not contain these additives.

It should be understood that even though the additives discussed abovehave been referred to by their "pure" chemical formulae, some levels oramounts of impurities may be acceptable, so long as the impurities donot interfere significantly with the processes of the invention orcontribute undesirable by-products to the finished composite material.

Moreover, particular emphasis is placed upon modifying the properties ofa composite body which is produced by reactively infiltrating a masscontaining boron carbide with a zirconium parent metal (hereinaftersometimes referred to as a "ZBC composite body"). However, the methodsdisclosed herein are believed to be generic for a number of differentparent metals (e.g., titanium, zirconium, tantalum, hafnium, etc.) whichmay be reactively infiltrated into (1) a mixture of boron carbide and aboron donor material and/or a carbon donor material and (2) a mixture ofa boron donor material and a carbon donor material.

DEFINITIONS

As used in this specification and the appended claims, the terms beloware defined as follows:

"Parent metal" refers to that metal, e.g. zirconium, titanium, hafnium,etc., which is the precursor to the polycrystalline oxidation reactionproduct, that is, the parent metal boride, parent metal carbide, parentmetal nitride, or other parent metal compound, and includes that metalas a pure or relatively pure metal, a coninercially available metalhaving impurities and/or alloying constituents therein, and an alloy inwhich that metal precursor is the major constituent; and when a specificmetal is mentioned as the parent metal, e.g. zirconium, titanium,hafnium, etc., the metal identified should be read with this definitionin mind unless indicated otherwise by the context.

"Parent metal boride" and "parent metal boro compounds" mean a reactionproduct containing boron formed upon reaction between a boron donormaterial, such as boron carbide or boron nitride, and the parent metaland includes a binary compound of boron with the parent metal as well asternary or higher order compounds.

"Parent metal nitride" means a reaction product containing nitrogenformed upon reaction of a nitrogen donor material, such as boron nitrideand the parent metal.

"Parent metal carbide" means a reaction product containing carbon formedupon reaction of a carbon donor material, such as boron carbide, and theparent metal.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a schematic elevational view in cross-section showing amodified B₄ C preform 2 in contact with an ingot of zirconium parentmetal 3, both of which are contained within a refractory vessel 1;

FIG. 2 is a schematic elevational view in cross-section showing a B₄ Cpreform 2 in contact with a zirconium sponge parent metal 3, both ofwhich are contained within a refractory vessel 1;

FIG. 3 is a schematic elevational view in cross-section showing a B₄ Cmaterial 101 in contact with a parent metal 103, both of which arecontained within a graphite crucible 102;

FIG. 4 is a photomicrograph taken at about 1000× of a microstructure ofa sample produced in accordance with Example 5;

FIG. 5 is a photomicrograph taken at about 1000× of a microstructure ofa comparative sample produced in accordance with FIG. 1 of U.S. Pat. No.4,885,130 (i.e., no niobium was included);

FIG. 6 is a photomicrograph taken at about 1000× of a microstructure ofa sample produced in accordance with Example 7;

FIGS. 7 and 8 are photomicrographs taken at about 400× and 1000×magnification, respectively, of sections of composite bodies formed inaccordance with Examples 8 and 9;

FIG. 9 is a photomicrograph taken at about 400× magnification, of theplatelet reinforced composite body fabricated in Example 10;

FIG. 10 is a schematic cross-section view of the setup employed infabricating the platelet reinforced composite body described in Example11;

FIG. 11 is a photomicrograph taken at about 400× magnification, of apolished cross-section of the platelet reinforced composite bodydescribed in Example 11;

FIG. 12 is a schematic cross-sectional view of the setup employed infabricating the platelet reinforced composites body described in Example13;

FIG. 13 is a photomicrograph of the ceramic composite bodies fabricatedin accordance with Example 14 after testing their oxidation resistance;

FIGS. 14 through 21 are photomicrographs taken at about 1000×magnification, of cross-sections of the composites formed according toExample 16;

FIG. 22 is a schematic cross-sectional view of the setup employed tofabricate the platelet reinforced composite extrusion die described inExample 17;

FIGS. 23a, 23b and 23c are top, bottom, and cross-sectional views,respectively, of the formed platelet reinforced composite extrusion die;and described in Example 17; and

FIGS. 24 through 28 are photomicrographs taken at about 1000×magnification, of cross-sections of the composites formed according toExample 18.

DETAILED DESCRIPTION OF THE INVENTION AND PREFERRED EMBODIMENTS

The present invention relates to methods for modifying the mechanicalproperties of a composite body which is produced by the reactiveinfiltration of a parent metal into a permeable mass containing, forexample, (1) boron carbide or (2) boron carbide and a boron donormaterial and/or a carbon donor material or (3) a boron donor materialand a carbon donor material. Particularly, by communicating at least oneadditive material with a boron and carbon-containing naterlal (e.g., B₄C) and/or with a parent metal at least at some polnt during the process,mechanical properties such as hardness, modulus of elasticity, density,porosity, and grain size may be adjusted advantageously. As disclosed inthe '433 Series, a baron carbide preform can be prepared by any of awide range of conventional ceramic body formation methods, includinguniaxial pressing, isostatic pressing, slip casting, sedimentatloncasting, tape casting, injection molding, filament winding for fibrousmaterials, etc. Additionally, It is disclosed that an initial bonding ofthe material comprising the preform, prior to reactive infiltration, mayoccur by such processes as light sintering of the materials, or by useof various organic or inorganic binder materials which do notsignificantly Interfere with the process or contribute undesirableby-products to the finished material. It has been discovered that by,(1) combining at least one additive material with the boron and/orcarbon containing material, (2) mixing or alloying at least one additivematerial wlth the parent metal, (3) placing at least one additivematerial at an interface between the parent metal and the mass of fillermaterial or preform, (4) or any combination of these methods, can resultin a potentially desirable modification of the properties of theresultant composite body. For example, additive materials such as TaC,ZrC, SiC, ZrB₂, VC, NbC, WC, W₂ B₅ and/or Mo₂ B₅ can be combined withthe boron and/or carbon containing material (e.g. boron carbide) and canbe shaped or formed to result in a prefom which has sufficient shapeintegrity and green strength; is permeable to the transport of moltenmetal; preferably has a porosity of between about 5-90 percent byvolume, and more preferably has a porosity between about 25-75 percentby volume. Further, an additive material may comprise at least one ofthe following refractory oxides: alumina (Al₂ O₃), magnesia (MgO),spinel (MgAl₂ O₄), yttria (Y₂ O₃), lanthanum oxide (La₂ O₃), calciumoxide (CaO), hafnium oxide (HfO.sub. 2), ytterbium oxide (Yb₂ O₃),zirconium (ZrSiO₄) borides of silicon (e.g., SiB₆, SiB₄), etc. Furtherstill, additive materials comprising refractory oxides such as ZrO₂,stabilized ZrO₂, etc., may be admixed with the boron and/orcarbon-containing material to form the permeable mass to be reactivelyinfiltrated in order to enhance the creep-resistance of the formedcomposite body.

In one embodiment of the invention, the ratio of parent metal-boride toparent metal-carbide within the formed composite may be altered orcontrolled by utilizing an additive material comprising reducible metalborides or reducible metal carbides in addition to a mass comprisingboron carbide. Specifically, one or more reducible additive compoundssuch as SiB₆, SiC, Mo₂ B₅, W₂ B₅, TaB₂, etc., can be provided by, forexample, admixing powders of the reducible additive compounds with theboron and/or carbon containing powders (e.g. B₄ C) to produce thepermeable mass which is to be contacted with molten parent metal. Themolten parent metal may react with the carbon and/or boron constituentof the reducible compound(s) to form a parent metal boride or carbidewhich can liberate elemental reduced metal (e.g., Mo, W, etc.). Theliberated metal may alloy with residual parent metal, form anintermetallic compound with the parent metal, be present as an unreactedor elemental phase within the formed composite, etc.

Moreover, metallic additive materials such as Al, Nb, Ni, Ti, Hf, Si, V,Ta, Co, Cr, Mo, W and alloys thereof, etc., can be communicated with, atleast at some point during the process, at least one of the parent metaland/or some portion of the permeable mass which is to be reactivelyinfiltrated. For example, an additive metal comprising niobium may bealloyed with, for example, a zirconium parent metal in an amount of0.5-10 percent by weight, and preferably, 1-5 percent by weight.Further, depending upon the process conditions (e.g., temperature) andthe reactive infiltration system (i.e., combination of parent metal,permeable mass, atmosphere, etc.), a metal such as titanium can serve asboth a parent metal and an additive (e.g., a zirconium parent metal mayreactively infiltrate into a permeable mass (e.g., a preform) comprisinga mixture of boron carbide and titanium (i.e., wherein titaniumfunctions as an additive material), whereas under differing processconditions titanium may function as a parent metal and reactivelyinfiltrate into a permeable mass comprising boron carbide). The relativequantity of the particular metal present may also affect which metalfunctions primarily as the parent metal (e.g., a metal having thegreater quantity corresponds to the parent metal as defined herein).However, the additive may also react with the permeable mass to formadditive carbide and/or additive boride phases. For example, an additivemetal (e.g., niobium, titanium, etc.) may be present in the ceramicand/or metallic phase of the formed composite.

Moreover, other materials, such as, for example titanium diboride andaluminum dodecaboride, may also be included in the permeable mass whichis to be reactively infiltrated. These materials, under certainprocessing conditions, may function as filler materials, so long as theydo not adversely impact resultant mechanical properties of the compositebody or the formation of the composite body.

An additive material may be admixed with a filler material to form apermeable mass (e.g., a preform). However, in most cases, the additivematerial should be relatively more reactive in comparison to the fillermaterial. Particularly, the characteristics of an additive material in aspecific reactive infiltration system are distinct from those of afiller material. For example, an additive material (e.g., niobium) maybe capable of altering the morphology of the microstructure (e.g.,achieving a smaller or refined microstructure) of a body formed byreactive infiltration. Further, an additive material (e.g., a refractoryoxide) may be capable of increasing the creep resistance of a bodyformed by reactive infiltration (e.g., a refractory oxide may tend topin or lock together phases within the formed body). Further still, anadditive material may function as a nucleation site for precipitation ofthe products (e.g., ZrB₂) formed by reactive infiltration. In contrast,a filler material tends to be relatively inert during the reactiveinfiltration process. Moreover, the ability of a material to function asan additive material or filler material is dependent upon the processingconditions (e.g., temperature) and particular reactive infiltrationsystem (e.g., parent metal, atmosphere, other constituents in thepermeable mass, etc.). Therefore, upon proper selection of additivematerials and processing conditions, the present invention permitsmodifying or tailoring the characteristics of a body formed by reactiveinfiltration.

Further, an additive material (e.g., SiB₆) may react to form one or morephases (e.g., SiO₂) which renders at least the portion of the formedcomposite body more oxidation resistant. Specifically, an additivematerial comprising silicon hexaboride may react upon exposure to anoxygen-containing environment at an elevated temperature to form anoxidation resistant layer comprising silicon (e.g., amorphous SiO₂) uponat least a portion of a surface region of the formed body (e.g., a ZBCbody formed by reactive infiltration can be formed so as to contain asurface layer, at least a portion of which comprises SiO₂).

Further still, it is possible that the additive material may beincorporated within a phase or phases (e.g., ZrC, ZrB₂, etc.) and/orbetween grain boundaries, which were formed during reactive infiltration(e.g., a particle of ZrC at least partially incorporated within a phasecomprising ZrC which has formed by reactive infiltration). Withoutwishing to be bound by any specific theory or explanation, it ispossible that when the additive material is present between grainboundaries, the additive material may function to lock or pin togetheradjacent phases and therefore, enhance high temperature creepperformance. Moreover, the additive material may function to modify themorphology of the formed composite (e.g., by achieving a refinedmicrostructure, precipitated phases, etc.).

By following the general processing procedures set forth in the '433Series, and by utilizing a setup in accordance with, for example, FIG. 3herein, it has been discovered that properties of a composite body canbe modified by communicating an appropriate additive material (e.g., Nb,TaC, SiB₆, etc.) with the parent metal and/or permeable mass (e.g.,boron carbide) at least at some point during the process. For example,boron carbide combined with an appropriate additive material, which,optionally, may be further combined with any desired inert fillermaterials, can be fabricated into a preform with a shape correspondingto an approximate desired geometry of the final composite. For example,as shown in FIG. 3, a mass comprising boron carbide 101, is locatedwithin a graphite crucible 102, with a parent metal 103, in contacttherewith. Additionally, the boron carbide material 101, may comprise aloose bed of boron carbide or may be formed into a preform which can beprepared by any of a wide range of ceramic body formation methods (e.g.,uniaxial pressing, isostatic pressing, slip casting, sedimentationcasting, tape casting, injection molding, spray coating, tapping,dipping, extruding, filament winding for fibrous material, etc.)depending on the specific characteristics of the filler. Initial bondingof the permeable mass prior to achieving a reactive infiltration intothe permeable mass, may be obtained through light sintering or by use ofvarious organic or inorganic binder materials which do not significantlyinterfere with the reactive infiltration process or contributeundesirable by-products to the finished material. The preform may bemanufactured to have sufficient shape integrity and green strength, andshould be permeable to the transport of molten metal, and preferablyhave a porosity of between about 5 and 90 percent by volume and morepreferably about 25-75 percent by volume. Moreover, suitable fillermaterials for use in the permeable mass may includer for example,titanium diboride, aluminum dodecaboride, etc., provided that thesematerials are relatively inert under the process conditions (e.g.,certain filler materials may be induced to function as an additivematerial if the reactive infiltration process conditions areappropriately altered). Suitable particulates for use as fillers in thepermeable mass typically have a mesh size of from about 14 to about1000, but any suitable mixture of filler materials and mesh sizes may beused. The boron carbide material 101, is then contacted with moltenparent metal, on one or more of its surfaces, for a time sufficient tocomplete reactive infiltration to the surface boundaries of the boroncarbide material 101. The result of this process is a ceramic-metalcomposite body of a shape closely or substantially exactly duplicatingthe shape of the boron carbide material 101, thus minimizing oreliminating the expense of final machining or grinding operations.

It has been discovered that by admixing about 5-50 percent by weight ofan additive material (e.g., TaC, ZrC, or ZrB₂, etc.) having a puritylevel of at least about 99%, with a boron source material and a carbonsource material (e.g., boron carbide) and a suitable binder material,such as an organic or an inorganic binder, and forming a preform inaccordance with the methods set forth in Patent '130, and thereafterreactively infiltrating a molten parent metal into the preform, theamount of porosity in a resultant composite body, relative to acomposite body which does not utilize the aforementioned additivematerials, is reduced.

Moreover, by cormnunicating at least one of the metallic additivematerials (e.g., Ti, Si, Al, Cr, Nb, etc.) with the parent metal and/orthe permeable mass, by any of the methods discussed above, at least oneproperty of a formed composite body can be modified relative to acomposite body which does not include such an additive. For example, ifthe parent metal comprises a zirconium metal, a metallic additivematerial such as niobium could be alloyed with the zirconium parentmetal. The zirconium-niobium alloy could then be contacted with, forexample, a boron carbide material which could be shaped or formed into apreform, or could be a loose mass or bed of particulate. When thezirconium niobium alloy is made molten in the presence of asubstantially inert environment, the molten metal reactively infiltratesthe boron carbide mass to form at least one reaction product. Forexample, the boron carbide can be decomposed or reduced, at least inpart, by the molten zirconium parent metal, thereby forming, forexample, a zirconium diboride compound. Additionally, a zirconiumcarbide may also be produced. Moreover, in some cases a zirconium-boroncompound may also be produced. As initial reaction product is formed byreactive infiltration, at least a portion of the formed reaction productis maintained in contact with the zirconium parent metal, and additionalmolten parent metal is drawn or transported through unreacted boroncarbide by a wicking or a capillary action. The transported zirconiummetal forms additional zirconium metal boride (e.g., zirconiumdiboride), zirconium metal carbide (e.g., zirconium carbide) and/orzirconium metal boro carbide and the formation or development of aceramic body is continued until either the zirconium metal or boroncarbide has been consumed, or until the reaction temperature is alteredto be outside of the reaction temperature envelope. Preferably,conversion of the boron carbide to the parent metal boride and/or parentmetal carbide and optionally parent metal boro carbide is at least about50 percent, and most preferably at least about 90%. In certainsituations, it may be desirable to obtain substantially completereaction of the boron carbide, which can be achieved by the techniquesof the present invention.

Moreover, the presence of an additive material comprising niobium whenalloyed into the zirconium parent metal, particularly when the weightpercent of niobium in the zirconium alloy is about 1-5 weight percent,may result in a self-supporting body which displays a reduction in grainsize relative to a self-supporting body produced by utilizing azirconium parent metal having little or no niobium present. In addition,it has been observed that the relative amount of zirconium metal thatinfiltrates into a permeable mass comprising a boron source material anda carbon source material (e.g., boron carbide) can be enhanced, and/orthe rate of infiltration can be increased, thus resulting in asubstantially low (e.g., less than 5 volume percent) residual metalcontent in the as-grown or as-formed self-supporting body (e.g., theniobium constituent of the alloy may increase the fluidity of thezirconium). The reduction in grain size and/or volume percent ofresidual metal present in the self-supporting composite bodies which maybe formed according to one aspect of the invention, can result inplatelet reinforced bodies which demonstrate improved high temperatureperformance in such areas as strength, oxidation resistance andcorrosion resistance, in comparison to similar bodies made withoututilizing niobium alloyed with the zirconium parent metal. Withoutwishing to be bound by any specific theory or explanation, it isbelieved that niobium may be present in the formed ceramic and/or theresidual metallic constituent, which exists between platelets ofzirconium diboride and/or between particles of zirconium carbide.Particularly, when such niobium is present in the residual metallicconstituent contained within the self-supporting composite body, theresidual metallic constituent may exhibit better mechanical propertiesrelative to a similar body which contains residual metallic constituentwithout niobium. The amount of niobium in the residual metallicconstituent may be from about 1/2 percent to about 25 percent by weightand a preferable range may be about 2-5 percent by weight. Additionally,a refinement in grain size of the formed microstructure may be achievedby utilizing an additive such as niobium in combination with a parentmetal such as zirconium.

Further, niobium, as well as other suitable additive materials, may beprovided as at least one alloying constituent, within the permeable massto be reactively infiltrated, as well as at the interface between theparent metal and the permeable mass to be reactively infiltrated.Further still, an additive material (e.g., TaC, SiB₆, MgO, etc.) may beadmixed with at least one other additive materials such as additivemetal materials (e.g., Nb, Co, Ni, V, etc.) and at least one fillermaterial to form the permeable mass which is to be reactivelyinfiltrated. For example, a permeable mass comprising boron carbide, afiller material, an additive material (e.g., TaC), and an additive metal(e.g., Si) may be reactively infiltrated with a zirconium parent metalalloy which contains niobium.

The following are examples of various aspects of the present invention.These examples are intended only to be illustrative of preferredembodiments of the present invention which are directed to utilizingvarious additive materials and are not intended to limit the scope ofthe invention.

EXAMPLES 1-3

A preform of boron carbide measuring about 1-inch (25 mm) in diameterand about 3/8-inch (9.5 mm) thick was made by admixing about 85 percentby weight B₄ C (1000 grit from ESK), about 5 percent by weight organlcbinder (Acrawax-C from Lonza, Inc.) and about 10 percent by weight TaC(from Atlantic Equipment Engineers). The admixture was placed in a steeldie and dry pressed at a pressure of about 2000 psi (14 MPa). As shownin FIG. 1, the preform 2 was placed in a bottom portion of a graphiterefractory vessel 1 (made from Grade ATJ graphite from Union Carbide)and placed in contact with an ingot of zirconium parent metal 2 (Grade702 Zr alloy from Teledyne Wah Chang Albany). The graphite refractoryvessel, together with its contents, was placed in a controlledatmosphere-resistance heated furnace. The atmosphere in the furnace wasargon, the argon being from Matheson Gas Products, Inc. The furnace wasfirst evacuated at room temperature to a pressure of about 1×10⁻² Torr(1.3 Pa) and thereafter backfilled with argon. The furnace was thenevacuated to a pressure of about 1×10⁻² Torr (1.3 Pa) and thereafterheated from about room temperature to a temperature of about 250° C.over a period of about 30 minutes. The furnace was thereafter heatedfrom about 250° C. to about 460° C., at a rate of 100° C. per hour. Thefurnace was again backfilled with argon which remained flowing at a rateof about 0.5 liter per minute and was maintained at a pressure of about2 psi (14 kPa). The furnace was heated to a temperature of about 1950°C. for about two-hours and then held at about 1950° C. for about twohours. The furnace was then cooled for about five hours. After cooling,the formed composite was removed from the furnace.

The resulting composite body was examined, and it was discovered thatthe amount of porosity in the bottom one-fourth of the composite body(i.e., the portion of the body which was initially the most distant fromthe ingot of parent metal) had been reduced relative to the amount ofporosity in composites produced by an identical method (i.e., all stepswere identical, except for the presence of TaC in the preform). Statedin greater detail, the composite bodies produced without incorporatingTaC into the preform typically exhibited a substantial amount ofporosity at an interface 4 between the bottom surface of the preform 2and the refractory vessel 1. However, such porosity was substantiallycompletely eliminated by practicing the methods according to the presentinvention.

The procedures set forth above were followed substantially exactly forExamples 2 and 3, except that rather than utilizing TaC as an additive,ZrC and ZrB₂ were used as additives, respectively, to the boron carbidepreform. Particularly, each of ZrC and ZrB₂ (also obtained from AtlanticEquipment Engineers) was individually added to the boron carbidematerial forming the preform in an amount which was about 10 percent byweight. After following the processing steps set forth in Example 1above, it was observed that the porosity in the resultant compositebodies was substantially completely eliminated.

A second aspect of the present invention relates to substantiallycompletely eliminating the porosity which occurs at an interface betweena boron carbide preform and a graphite refractory vessel by using adifferent parent metal zirconium alloy than that used in the aboveexamples and that used in the '433 Series. Particularly, the aboveexamples and the '433 Series disclose the use of a commerciallyavailable Grade 702 zirconium alloy. However, it has been unexpectedlydiscovered that in some cases, the use of the Grade 702 alloy may bedetrimental to the resultant composite body because the Grade 702 alloycontains about 0.1-0.2 weight percent tin (i.e., 1000-2000 ppm by weighttin). The presence of tin in these amounts has been discovered to beundesirable because it appears that as a boron carbide permeable mass isreactively infiltrated by the Grade 702 parent metal alloy, the zone ofmetal at the infiltration front becomes enriched in tin. This zone orlayer of tin-rich metal accumulates at or adjacent to the interfacewhich exists between the bottom of the permeable mass and the graphiterefractory vessel (i.e., at or adjacent to the interface 4 in FIG. 1).It appears that this layer of tin volatilizes at the interface 4,resulting in porosity In the composite body. This problem can beameliorated by utlllzing a zirconium sponge parent metal containing lessthan 1000 ppm by weight tin, preforably less than 500 ppm by weight tin.Thus, by utilizing a parent metal of zirconium sponge from Teledyne WahChang Albany, having a tin content of about 200 ppm, the amount ofporosity produced at the interface 4 is substantially completelyeliminated. Thus, the added costs of grinding or machining can beeliminated.

The following is an example of the second aspect of the presentInvention. The example is intended to be illustrative of various aspectsof the effect of utilizing a zirconium sponge parent metal forreactively infiltrating a boron carbide preform.

EXAMPLE 4

A boron carbide preform was manufactured according to the steps setforth in Examples 1-3. However, the composition of the preform was about95 percent by weight boron carblde and about 5 percent by weight organicbinder (Acrawax C from Lonza, Inc.).

As shown in FIG. 2, the boron carbide preform 2 was placed in a bottomportion of a graphite refractory vessel 1 and the boron carbide preform2 was placed in contact wlth a zirconium sponge parent metal 3. Thegraphite refractory vessel, together with its contents, was placed in aclosed atmosphere-resistance heating furnace. The atmosphere in thefurnace was argon, the argon being from Matheson Gas Products, Inc. Thefurnace was first evacuated at room temperature to a pressure of about1×10⁻² Torr (1.3 Pa) and thereafter backfilled with argon. The furnacewas then evacuated to a pressure of about 1×10⁻² Torr (1.3 Pa) andthereafter heated from about room temperature to a temperature of about250° C. over a period of about 30 mlnutes. The furnace was thereafterheated from about 250° C. to about 450° C., at a rate of 100° C. perhour. The furnace was agaln backfilled with argon which remained flowingat a rate of about 0.5 liter per minute and was maintained at a pressureof about 2 psi (14 kPa). The furnace was heated to a temperature ofabout 1950° C. ever a two-hour period and then held at about 1950° C.for about two hours. The furnace was then cooled for about five hours.After cooling, the formed composite was removed from the furnace.

The resulting composite body was examined, add it was discovered thatthe amount of porosity In the composite body had been reduced relativeto the amount of porosity in composites produced by an identical method,except for the use of a Grade 702 zirconium alloy. Stated in greaterdetail, the composite bodies produced by using a Grade 702 zirconiumalloy typlcally exhibited a substantial amount of porosity at theinterface between the preform 2 and refractory vessel 1 at the interfacedesignated 4. However, such porosity was substantially completelyeliminated by utillzlng a zirconium sponge parent metal having arelatively low tin content.

EXAMPLE 5

FIG. 3 shows a setup in cross-section which was used to form a plateletreinforced composite by reactive infiltration in accordance with is thepresent invention. In order to create a preform 101, about 90 grams of aslurry comprising about 39.8 wt % 1000 grit B₄ C (MIO from ESK Company),59.8 wt % methylene chloride (from J. T. Baker) and 0.4 wt % of a binderXUS 40303.00 from Dow Chemical Company was mixed and then poured into a2 inch (51 mm) by 2 inch (51 mm) by 3 inch (76 mm) graphite mold 102(ATJ from Union Carbide). The solvent was evaporated from the preform101 at room temperature in approximately 18-24 hours in a vented dryingbox. After the evaporation step, the prefore 101 had approximatedimensions of about 2 inches (51 mm) by 2 inches (11 mm) by 1/2 inch (13mm).

The binder was removed from the preform 101 by placlng the graphite mold102 containing the preform 101 into a vacuum furnace, evacuating thefurnace to approximately 2×10⁻⁴ torr (0.027 Pa) and backfilllng at roomtemperature with argon to approximately 2 psi (14 kPa) pressure. At thispoint, the furnace was again evacuated to a low vacuum (approximately1×10⁻¹ torr (13 Pa))and then backfilled with argon at a gas flow rate ofapproximately 1000 cc per minute until the pressure within the furnacewas approximately 2 psi (14 kPa). After this second evacuation andbackfilling step, the furnace was again evacuated to a low vacuum(approximately 1×10⁻¹ torr (13 Pa)) and backfilled with argon at roomtemperature to approximately 2 psi (14 kPa). These multiple evacuationand backfilling steps were performed to ensure a substantially pureargon atmosphere within the furnace. After the third evacuation andbackfilling step was completed, a continuous argon gas flow rate ofapproximately 1000 cc per minute and a furnace pressure of about 2 psi(14 kPa) was maintained in the furnace. The furnace temperature was thenramped from room temperature to about 350° C. in 2.5 hours, then rampedfrom about 350° to about 450° C. at about 10° C. per hour, then fromabout 450° to about 600° C. in about 3 hours, then held at about 600° C.for about 1 hour. The setup was ramped down to about room temperature inapproximately 2 hours. After reaching room temperature, the graphitemold 102 containing the preform 101 was removed from the furnace.

An approximately 219.60 gram ingot 103 of comercially availableZircadyne 705 zirconium allay, which contained niobium as an alloyingconstituent, was obtained from Teledyne Wah Chang of Albany, Ore., andhaving dimensions of about 1.98 inch (50 mm) by 1.98 inch (50 mm) by 1/2inch (13 mm) was placed on top of the preform 101 contained within thegraphite mold 102. The setup 104, consisting of the graphite mold 102and its contents, was placed into a vacuum furnace at room temperature.The furnace was then evacuated to approximately 2×10⁻⁴ torr (0.027 Pa)and backfilled at room temperature with argon until the pressure withinthe furnace was approximately 2 psi (14 kPa). At this point, the furnacewas again evacuated to approximately 2×10⁻⁴ torr (0.027 Pa) and thenbackfilled with argon until the pressure within the furnace wasapproximately 2 psi (14 kPa). This second evacuation and backfillingstep was performed to ensure a pure argon atmosphere withln the furnace.

After the second backfilling step, the argon gas flow rate to thefurnace was maintained at approxlmately 2 liters/minute and the furnacepressure was maintained at approximately 2 psi (14 kPa). The furnacetemperature was then ramped to about 1950° C. in about 5 hours. Thefurnace temperature was maintained at about 1950° C. for about 2 hoursand then ramped down to room temperature in about 8 hours. Afterreaching room temperature, the setup 104 was removed from the furnaceand disassembled. A platelet reinforced composlte comprising zlrconiumdiborlde, zirconium carbide, and the niobium containlng zirconium alloy,was recovered. FIG. 4 is a photomicrograph taken at about 1000× of theplatelet reinforced composite produced in the present example. As shownin FIG. 4, the zirconium diboride phase Is labelled 108, the zirconiumcarbide phase is labelled 110, and the residual niobium-containlngzirconium alloy is labelled 112. FIG. 5 is a photomicrograph taken atabout 1000× of a platelet reinforced composite produced by a methodwhich is substantially similar to the method used to produce thecomposite shown in FIG. 4 (i.e., produced in accordance with Example 1in Patent '130). Thus, the ccmposite shown in FIG. 5 was produced from azirconium ingot which contained substantially no niobium. A comparisonof the composite microstructures shown in FIGS. 4 and 5 demonstratesthat the composite shown in FIG. 4 has a finer microstructure and lessresidual zirconium parent metal than the composite shown in FIG. 5.

Accordingly, this Example demonstrates that it is possible to refine themicrostructure of a platelet reinforced zirconium composite by utilizinga zirconium alloy as the parent metal which contains niobium as anadditive material.

EXAMPLE 6

Example 6 was carried out with a setup as shown in FIG. 3 to form aplatelet reinforced composite by reactive infiltration in accordancewith the method of the present Invention. In order to create thepreform, approximately 77 grams of a slurry comprising about 39.8% byweight B₄ C (lot M10, from ESK Company), 59.8% by weight of methylenechloride (from J. T. Baker), and about 0.4% by weight of a binder XUS40303.00 from Dow Chemical Company was mixed and then poured into a 2inch (51 mm) by 2 inch (51 mm) by 3 inch (76 mm) graphite mold (ATJ fromUnion Carbide). The solvent was evaporated from the preform by placingthe graphite mold and its contents in a vented drying box at roomtemperature for approximately 18-24 hours. After the evaporation step,the preform had approximate dimensions of about 2 inches (51 mm) by 2inches (51 mm) by 1/2 inch (13 mm).

The binder was removed from the preform by placing the graphite moldcontaining the preform into a vacuum furnace, evacuating the furnace toa low vacuum (approximately 1×10⁻¹ torr (13 Pa)) and backfilling at roomtemperature wlth argon to approximately 2 psi (14 kPa). At this point,the furnace was again evacuated to approximately 1×10⁻¹ torr (13 Pa) andthen backfilled with argon at room temperature to approximately 2 psi(14 kPa). After this second evacuation and backfilling step, tha furnacewas again evacuated to approximately 1×10⁻¹ torr (13 Pa) and backfilledwith argon at room temperature to approximately 2 psi (14 kPa). Thesemultiple evacuation and backfilling steps were performed to ensure asubstantially pure argon atmosphere within the furnace. After the thirdevacuation and backfilllng step was completed, a continuous argon gasflow rate of approximately 1000 cc per minute and a furnace pressure ofabout 2 psi (14 kPa) w4s maintained in the furnace. The furnacetemperature was then ramped from room temperature to about 3500° C. inabout 2.5 hours, held at about 350° C. for about 2 hours, and thenheated from about 350° C. to about 450° C. at about 10° C. per hour.Upon reaching 450° C., the heating rate was changed and the furnacetemperature was raised from about 450° C. to about 500° C. in threehours. The furnace temperature was held at about 600° C. for about threehours and then cooled to room temperature in about two hours. Afterreaching room temperature, the setup was removed from the furnace.

An approximately 218.84 gram ingot of commercially available Zircadyne705 zirconium alloy, which contained niobium as an alloying constituent,was obtained from Teledyne Wah Chang of Albany, Ore., and havingapproximate dimensions of 2 inches (51 mm) by 2 inches (51 mm) by 1/2inch (13 mm) was placed on top of the preform contained within thegraphite mold. The setup, consisting of the graphite mold and itscontents, was placed into a vacuum furnace at about room temperature.The furnace was then evacuated to approximatelv 2×10⁻⁴ torr (0.27Pa) andbackfilled at room temperature with argon until the pressure within thefurnace was approxlmately 2 psi (14 kPa). At this point, the furnace wasagain evacuated to approximately 2×10⁻⁴ torr (0.027 Pa) for about oneminute, and then to about 3.6×10⁻⁴ torr (0.048 Pa). After thisevacuation step, the furnace was backfilled with argon until thepressure in the furnace was approximately 2 psi (14 kPa). This secondevacuation and backfilling step was performed to ensure a substantiallypure argon atmosphere within the furnace. After this second backfillingstep, the argon gas flow rate was maintained at approximately 2liters/minute and the furnace pressure was maintained at approximately 2psi (14 kPa). The furnace temperature was then ramped to approximately1900° C. in about five hours. The system was maintained at about 1900°C. for about 10 minutes, then the temperature in the furnace was rampeddown to room temperature in approximately 12 hours. After reaching roomtemperature, the setup was removed from the furnace and disassembled. Aplatelet reinforced composite, comprising zirconium diborides zirconiumcarbide and a metallic phase comprising zirconium and niobium wasrecovered.

Due to the shorter time permitted for reactive infiltration, thecomposite formed in Example 6 possessed a higher metal content than thecomposite formed In Example 5.

EXAMPLE 7

Example 7 was carried out wlth a setup as shown In FIG. 3 to form aplatelet reinforced composite by reactive infiltration in accordancewith the method of the present invention. In order to create thepreform, about 90 grams of a slurry comprising about 40.0 weight percentof 1000 grit B₄ C (lot M9 from ESK Company), about 59.6 weight percentof methylene is chloride (DCM from J. T, Baker) and about 0.4 weightpercent of binder XUS 40303.00 from Dow Chemical Company was mixed andthen poured into a 3 inch (76 mm) by 3 inch (76 mm) by 3 inch (76 mm)graphite mold (ATJ from Union Carbide). The solvent was removed from thepreform by placing the graphite mold and its contents in a vented dryingbox at room temperature for approximately 18-24 hours. After theevaporation step, a preform had approximate dimensions of about 3 inches(76 mm) by 3 inch as (76 mm) by 0.5 inch (13 mm).

The binder was removed from the preform by placing the graphite moldcontaining the preform into a vacuum furnace, evacuating the furnace toa low vacuum (approximately 1.0×10⁻¹ torr (13 Pa)) and backfilling atroom temperature wlth argon to approximately 2 psi (14 kPa). At thispoint, the furnace was again evacuated to approximately 1.0×10⁻¹ torr(13 Pa) and then backfilled with argon at room temperature toapproximately 2 psi (14 kPa). The two evacuation and backfilling stepswere performed to ensure a substantially pure argon atmosphere withinthe furnace. After the second evacuation and backfilling stop wascompleted, a continuous argon gas flow rate of approximately 2liters/minute and a furnace pressure of about 2 psi (14 kPa) wasmaintained in the furnace. The furnace temperature was then ramped fromroom temperature to about 200° C. in about two hours, held at about 200°C. for about two hours, and then heated from about 200° to about 350° C.at about 20° C. per hour. Upon reaching 350° C., the heating rate waschanged and the furnace temperature was raised from about 350° C. toabout 450° C. in about two hours. After the furnace temperature reached450° C., the setup was cooled to room temperature in approximately 12hours. Upon reaching room temperature, the setup was removed from thefurnace.

An approximately 581.69 gram ingot of comercially available Zircadyne705 zirconium alloy, which contained niobium as an alloying constituent,was obtained from Teledyne Wah Chang of Albany, Ore., and havingapproxlmate dimensions of 3 inch (76 mm) by 3 inch (76 mm) by 0.5 inch(13 mm) was placed on top of the preform contained within the graphitemold. The setup, consisting of the graphite mold and its contents, wasplaced into a vacuum furnace at room temperature. The furnace was thenevacuated to approximately 1×10⁻⁴ torr (0.013 Pa). The system was heatedfrom room temperature to about 1000° C. under vacuum in approximately 3hours. The furnace was then backfilled with argon gas flowing at a rateof about 2 liters/minute, until the pressure within the furnace wasapproximately 2 psi (14 kPa). The furnace was then heated from about1000° C. to about 1900° C. In approximately 3 hours and maintained atabout 1900° C. to about 2000° C. for about two hours. After holding thefurnace temperature in this range for about two hours, the furnace wasramped to room temperature in approxlmately 8 hours. Upon reaching roomtemperature, the setup was removed from the furnace and disassembled. Aplatelet relnforced composite comprising zirconium diboride, zirconiumcarbide and residual alloy comprising zirconium and niobium, wasrecovered. FIG. 6 is a photomicrograph taken at about 1000× of theplatelet reinforced composite produced in the present example. As shownin FIG. 6, the zirconium diboride phase is labelled 120, the zlrconiumcarbide phase is labelled 122, and the residual alloy comprisingzirconium and niobium is labelled 124. As in Example 5, a comparison ofthe composite microstructures shown in FIGS. 5 and 6 demonstrates thatthe composite shown in FIG. 6 has a finer microstructure and lessresidual zirconium parent metal than the composite shown in FIG. 5.

EXAMPLE 8

This Example demonstrates that an additive material comprising niobiummay be added to the permeable mass which is to be reactivelyinfiltrated.

FIG. 3 shows a lay-up in cross-section which was utilized to form acomposite in accordance with the present invention. About 28 grams of1,000 grit B₄ C (from ESK, lot number M9-C) and about 12 grams of 325mesh niobium powder (Alfa Products, Morton Thiokol, lot number B24H)were mixed with about 60 grams of Methylene Chloride from (J. T. Baker)and about 0.4 grams of Dow experimental ceramic binder XUS40303.00.Specifically, the B₄ C and niobium powders were dry milled on aball-mill in a nalgene bottle for about 8 hours. A solution comprisingthe methylene chloride and Dow ceramic binder was then added to themixture of B₄ C and niobium powders to form a slurry. The nalgene bottlecontaining the slurry was placed onto the carriage of a Tyler SieveShaker and was vibrated for about a half an hour. The resultant slurrywas sediment cast into a graphite mold measuring about 2" (51 mm)×2" (51mm)×3" (76 mm) (supplied by ATJ). The graphite crucible containing theslurry was placed into a plastic bag and permitted to dry overnight. Thegraphite crucible was removed from the plastic bag and placed in an ovento dry for about one hour at 45° C. and at 70° C. for about two hours.The resultant preform weighed about 313 grams and measured about 2" (51mm)×2" (51 mm)×0.35" (9 mm) in thickness.

The binder was removed from the preform by placing the graphite cruciblecontaining the preform into a vacuum furnace. The furnace was twiceevacuated and backfilled with argon. During the subsequent heatingsteps, argon was passed through the furnace at a rate of about twoliters per minute. The temperature of the furnace was raised from roomtemperature to about 350° C. at a rate of about 100° C. per hour. Thetemperature was increased to about 450° C. at a rate of about 50° C. perhour. The temperature was increased to about 725° C. at a rate ofapproximately 100° C. per hour. This temperature was maintained forabout one hour. The furnace was cooled to room temperature. Afterreaching room temperature, the graphite mold containing the preform wasremoved from the furnace.

A zirconium sponge weighing about 171 grams supplied by WesternZirconium Co., nuclear grade lot 4825, was placed upon the preformcontained within the ATJ graphite mold. The lay-up consisting of thegraphite mold and its contents was placed into a vacuum furnace at roomtemperature. The furnace was evacuated and backfilled with argon. Thetemperature of the furnace was raised from room temperature to about1000° C. at a rate of approximately 190° C. per hour while under avacuum. The temperature of the furnace was increased to about 1900° C.at a rate of approximately 190° C. per hour. During the second heatingstep, argon was passed through the furnace at a rate of about two litersper minute which supplied a chamber or gage pressure of about two (2)psig (0.14 kg/cm²). The temperature of about 1900° C. was maintained forabout two hours. The temperature of the furnace was cooled to roomtemperature at a rate of about 160° C. per hour. After reaching roomtemperature, the lay-up was removed from the furnace and disassembled.It was discovered that the zirconium metal had reacted with the preformto form a composite comprising zirconium diboride, zirconium carbide andzirconium metal.

FIG. 7 is a photomicrograph of a section at 400× magnification of thecomposite produced in accordance with this Example.

The flexural strength of three specimens formed in accordance with thisExample was tested. The samples measured about 6.05 millimeters in widthand about 3.06 millimeters in depth. The particular specimen to betested was placed upon the lower span of a four-point bending apparatuswhich measured about 40.06 millimeters. The upper span of the four-pointbending apparatus, which measured about 19.93 millimeters, was broughtinto contact with the specimen to be tested in order to apply thetesting load or force, which was about 5000 pounds. The load was appliedat a rate of about 0.51 millimeter per minute. The mean flexuralstrength for the samples tested was about 670 MPa. The flexural strengthof two specimens at about 1000° C. was tested utilizing theabove-described testing conditions. The mean flexural strength for thetwo specimens was about 330 MPa. The fracture toughness of two specimensformed in accordance with this Example was tested utilizing the sameconditions as discussed above in the flexural test. The two specimensmeasured about 4.855 millimeters in width and about 6.02 millimeters indepth. The samples were notched, placed upon the lower span of thefour-point bending apparatus and the testing load was applied. The meanfracture toughness for the specimens tested was about 13 MPa.m^(1/2).The fracture toughness for two samples formed in accordance with thisExample was tested at about 1,000° C. The specimens tested measuredabout 4.83 millimaters in width and about 6.115 millimeters ln depth.The samples to be tested were placed upon the lower span of thefour-point bending apparatus and processed ln the manner discussedabove. The mean fracture toughness for the samples tested at about1,000° C. was about 15 mPa.m^(1/2). Further, the Young's Modulus forbodles formed in accordance with this Example was calculated to be inthe range from about 417 GPa through about 420 GPa.

EXAMPLE 9

This Example demonstrates that an additive material comprising istitanium may be added to the permeable mass to be reactivelyinfiltrated.

This Example was conducted substantially in accordance with Example 8with the exception that about 7.12 grams of -325 mesh tltanium metal(substantially all particle diameters smaller than about 45 μm) suppliedby Chemalloy Co. was utilized instead of the niobium powder, A slurrycomprlsing about 60 grams of methylene chloride, 0.4 grams of DowExperimental Ceramic Binder XUS 40303.00, about 7 grams of titaniumpowder, and about 33 grams of 1000 grit (average particle diameter ofabout 5 μm) B₄ C powder supplied by ESX Co. was sediment cast into a 2inch (51 mm) square ATJ graphite crucible. The binder was removed and azirconium sponge from Western Zirconium Co. (nuclear grade lot 4825)whlch welghed about 200 grams was placed upon the sediment cast preformin the ATJ graphite crucible. The crucible was placed into a vacuumfurnace and evacuated twice with argon and heated substantially inaccordance with Example 8. After heating and cooling to roomtemperature, the lay-up was removed from the furnace and disassembled. Aplatelet reinforced composite comprising zirconium diboride, zirconiumcarbide and a metal phase including zirconium and titanium wasrecovered.

FIG. 8 is a microphotograph taken at about 1000× magnification of asection formed in accordance with this Example.

The mechanical properties of three specimens formed in accordance withthis Example were tested utilizing the procedures discussed in Example8. The mean room temperature flexural strength was about 925 MPa. The1000° C. flexural test for two samples provided a mean flexural strengthof about 330 MPa. The fracture toughness for two samples, which wereformed in accordance with thls Example provided a mean fracturetoughness of about 17 MPa*m^(1/2). The fracture toughness at about1,000° C. for two samples provided a mean of about 14 MPa*m^(1/2).Further, the Young's Modulus was calculated and was found to averageabout 388 GPa.

EXAMPLE 10

Thls Example was conducted substantially in accordance with Example 8with the exception that about 2.5 percent of the preform by weightcomprlsed AESAR's aluminum powder (-325 mesh, substantially all particlediameters smaller than about 45 μm, 99.8 percent pure, Aesar Group ofJohnson Matthey Co., Seabrook, N.H).

Specifically, about 9.75 grams of 1000 grit TETRABOR® boron carbidepowder (5 μm average particle diameter, ESK Engineered Materials, NewCanaan, Conn.) and about 0.25 grams of aluminum powder were mixed withabout 12 grams of methylene chloride (J. T. Baker Co., Phillipsburg,N.J.) and about 0.1 grams of XUS 40303.00 Experimental Binder (DowChemical Co., Midland, Mich.) to form a slurry. Specifically, the boroncarbide and aluminum powders were dry milled on a ball mill in aNALGENEI® plastic jar (Nalge Co., Rochester, N.Y.) for about 8 hours. Asolulllon comprising the methylene chloride and the binder was thenadded to the mixture of boron carbide and aluminum powders to form aslurry. The resultant slurry was sediment last into a one inch (25 mm)diameter graphite crucible (Grade ATJ, Union Carbide Co., CarbonProducts Div., Cleveland, Ohio). The graphite crucible containing thecast slurry was placed into a plastic bag and permitted to dryovernight. The graphite crucible was then removed from the plastic bagand placed into an oven to dry for about 1 hour at a temperature ofabout 45° C. followed by an about 2 hour bake at a temperature of about70° C. The resultant preform assembly weighed about 40.6 grams andmeasured about 0.5 inches (13 mm) in thickness.

The binder was removed from the preform by placing the graphite cruciblecontaining the preform into a vacuum furnace. The furnace was twiceevacuated and backfilled with argon. During the subsequent heatingsteps, argon was passed through the furnace at a rate of about 2 litersper minute. The temperature of the furnace was raised from substantiallyroom temperature to a temperature of about 350° C. at a rate of about100° C. per hour. The temperature was then increased to about 450° C. ata rate of about 50° C. per hour. The temperature was then increased toabout 725° C. at a rate of about 100° C. per hour. After maintaining atemperature of about 725° C. for about 1 hour, power to the furnace wasinterrupted and the furnace was allowed to cool back to roomtemperature. After reaching substantially room temperature, the graphitecrucible containing the preform was removed from the furnace. The weightof the graphite crucible and its contents was about 40.5 grams. Thecalculated bulk density of the preform was about 1.41 grams per cubiccentimeter, which converts to about 56 percent of the theoreticaldensity of boron carbide.

About 53.9 grams of nuclear grade zirconium sponge (Western Zirconium,Ogden, Utah) was placed into a NALGENE® plastic jar (Nalge Co.,Rochester, N.Y.) and roll mixed for about 8 hours. After mixing, about3.7 grams of a binder solution comprising by weight about 0.8 percentXUS 40303.00 Experimental Binder (Dow Chemical Co.) and the balancemethylene chloride was added to the milled powder to form a slurry. TheNalgene jar and its slurry were then placed on an EBERBACH® shaker(Eberbach Corp., Ann Arbor, Mich.) and shaken for about one-half hour.The slurry of zirconium sponge and binder solution was then poured intothe graphite crucible. The graphite crucible and its contents were thenplaced into a drying box and allowed to dry overnight. The graphitecrucible and its contents was then placed into a drying oven at atemperature of about 45° C. After drying for about 1 hour at about 45°C., the drying was continued for about 2 hours more at a temperature ofabout 70° C. After drying, the graphite crucible and its contentsweighed about 94.4 grams.

The additional binder was removed in substantially the same manner aswas used to remove the original binder in the filler material.

The lay-up comprising the graphite mold and its contents was then placedinto a vacuum furnace at substantially room temperature. The furnace wasevacuated and backfilled with argon gas, and then evacuated one moretime. The temperature of the furnace was then raised from about roomtemperature to a temperature of about 1000° C. at a rate of about 210°C. per hour under vacuum. At a temperature of about 1000° C., thefurnace was backfilled with argon gas to a gauge pressure of about 2 psi(14 kilopascals). The temperature of the furnace was then increased fromabout 1000° C. to a temperature of about 1900° C. at a rate of about211° C. per hour. After maintaining a temperature of about 1900° C. forabout 2 hours, the temperature in the furnace was decreased to atemperature of about 500° C. at a rate of about 156° C. per hour. At atemperature of about 500° C., the flow rate of argon gas was increasedfrom about 2 liters per minute to about 10 liters per minute to increasethe rate of cooling. The temperature continued to decrease and, uponcooling to a temperature of about 100° C., the furnace was opened andthe lay-up was removed from the furnace and disassembled. It wasdiscovered that the zirconium metal had reacted with the preform to forma composite comprising zirconium diboride 130, zirconium carbide 132 andresidual metal 134 as shown in the photomicrograph of FIG. 9 which wastaken at approximately 400×.

EXAMPLE 11

This Example demonstrates that an additive metal comprising chromium maybe admixed with the permeable mass to be reactively infiltrated.

FIG. 10 shows a lay-up and cross-section which was utilized to form acomposite in accordance with this Example.

In order to create a preform by sedimentation casting, approximately32.4 grams of 1000 grit TETRABOR® boron carbide particulate (ESKEngineered Materials, New Canaan, Conn.) having an average particle sizeof about 5 microns was placed into an approximately 250 milliliterNALGENE® plastic bottle (Nalge Co., Rochester, N.Y.) along with about7.62 grams of chromium particulate (99.8% pure, Atlantic EquipmentEngineers Co., Bergenfield, N.J.) having a particle size ranging betweenabout 1 and about 5 microns in diameter and mixed together in a jar millfor about 8 hours. While the powders were being mixed, a binder solutioncomprising about 0.4 grams of XUS 40303.00 Experimental Binder (DowChemical Co., Midland, Mich.) and about 60 grams of methylene chloride(J. T. Baker Co., Phillipsburg, N.J.) was prepared. After the powdershad been mixed dry for about 8 hours, the binder solution was added tothe NALGENE® plastic bottle (Nalge Co., Rochester, N.Y.) to form aslurry. The bottle and lts contents were placed onto a EBERBACH® shaker(Eberbach Corp., Ann Arbor, Mich.) and shaken for about 1/2 hour. Afterthe slurry admixture 140 had been thoroughly shaken, the admixture wasthen poured into a Grade ATJ graphite mold 142 (Union Carbide Co.,Carbon Products Div., Cleveland, Ohio) the interior of which measuredabout 2 inches (51 m) square by about 31/4 lnches (83 mm) tall. Afterthe sediment had rigidized due to evaporative loss of much of themethylene chloride, the graphite mold 142 and its contents were thensealed in a ZIPLOC® plastic bag (Dow Brand, Indianapolis, Ind.) andallowed to to dry overnight. The plastic bag slowed the rate ofmethylene chloride evaporation so that the preform would not crack fromdifferential drying shrinkages. The following day the crucible and itscontents were removed from the plastic bag and placed into a drying ovenat a temperature of approximately 45° C. for a duration of about 1 hour.The temperature of the drying oven was then increased to about 70° C.and the graphite mold 142 and its contents were dried at thistemperature for about 2 hours. These drying operations removedsubstantially all of the methylene chloride vehicle. After drying, thesediment cast preform 140 had approximate dimensions of about 2 inches(51 mm) square by about 0.4 inches (10 mm) thick and weighed about 32.8grams.

The binder was removed from the preform by placing the graphite moldcontaining the preform into a vacuum furnace, evacuating the furnace toabout 30 inches (762 mm) of mercury vacuum (pressure less than about 133Pa.) and backfilling the furnace with argon gas to approximately 2 psig(14 kPag). Aftar repeating the evacuation and backfilling steps, anargon gas flow rate of about 2 liters per minute at a pressure of about2 psig (14 kPag) was established and maintained in the furnace. Thefurnace temperature was then increased from about room temperature to atemperature of about 350° C. at a rate of about 100° C. per hour. Uponreaching 350° C., the temperature was then increased to about 450° C. ata rate of about 50° C. per hour. Upon reaching 450° C., the temperaturewas increased to about 725° C. at a rate of about 100° C. per hour.After maintaining a temperature of about 725° C. for about 1 hour, thetemperature was decreased to about room temperature at a rate of about70° C. per hour. Upon cooling to about room temperature, the graphitemold 142 and its contents were removed from the furnace. The weight ofthe graphite mold 142 and its contents after firing was about 0.4 gramsless than the weight before firing. The dimensions of the mold andpreform were substantially unchanged. The bulk density of the preform140 computed to about 1.24 grams per cubic centimeter which converts toabout 42.8 percent of the theoretical density of boron carbide.

About 196.8 grams of zirconium sponge 144 (Nuclear Grade WesternZirconium Co., Ogden, Utah) parent metal was placed on top of thesediment cast preform 140 contained within the graphite mold 142. Thesetup comprising the graphite mold 142, the sediment cast preform 140 ,and the parent metal zirconium sponge 144 was then placed into a vacuumfurnace at about room temperature. The furnace was then evacuated toabout 30 inches (762 mm) of mercury vacuum (pressure less than about 133Pa) and then backfllled with argon gas to a pressure of about 2 psig (14kPag). This evacuation and backfilling procedure was then repeated.Following the is second backfilling with argon, the furnace chamber wasevacuated one more time to a final pressure of about 4×10⁻⁴ torr (0.053Pa). The furnace temperature was then increased from about roomtemperature to a temperature of about 1900° C. at a rate of about 210°C. per hour. Upon reaching a temperature of about 1000° C., the furnacechamber was backfilled with argon gas to a pressure of about 2 psig (14kPag) and a gas flow rate of about 2 liters per minute through thefurnace was established. The remainder of the run was conducted underthis argon atmosphere, After maintaining a temperature of about 1900° C.for about 2 hours, the furnace temperature was then decreased to about500° C. at a rate of about 150° C. per hour. Upon reaching a temperatureof about 500° C., the argon gas flow rate was increased from about 2liters per minute to about 10 liters per minute to assist in cooling thefurnace and the setup. The furnace was allowed to continue to cool. At atemperature of about 100° C., the furnace was opened and the setup wasremoved from the furnace and disassembled. A platelet reinforcedcomposite body had focmed. A mounted and diamond polished section of theformed composite body is shown in FIG. 11.

The microstructure reveals that the platelet reinforced compositecomprises zirconium diboride 150, zirconium carbide 152, and someresidual metal 154,

EXAMPLE 12

This Example illustrates utilizing an additive material comprisingparticulate silicon metal with a boron carbide preform to form aplatelet reinforced composite body. The setup employed is substantiallythe same as that shown in FIG. 10.

In order to create a preform by sedimentation casting approximately 9.2grams of 1000 grit TETRABOR® boron carbide powder (ESK EngineeredMaterials, New Canaan, Conn.) having an average particle size of about 5microns was placed into an approximately 250 milliliter NALGENE® plasticbottle (Nalge Co., Rochester, N.Y.) along with about 0.82 grams ofsilicon particulate (-325 mesh, Atlantic Equipment Engineers Co.,Bergenfield, N.J.) having substantially all particles smaller than about45 microns and mixed together by rolling onto a jar mill rack for about8 hours. While the powders were being mixed, a binder solutioncomprising about 0.1 grams of XUS 40303.00 Experimental Binder (DowChemical Co., Midland, Mich.) and about 12 grams of methylene chloride(J. T. Baker Co., Phillipsburg, N.J.) was prepared. After the powdershad been dry mixed for about 8 hours, the binder solution was added tothe NALGENE® plastic bottle and the bottle and its contents were placedonto an EBERBACH® shaker (Eberbach Corp., Ann Arbor, Mich.) and shakenfor about 1/2 hour. After the slurry had been thoroughly shaken, theadmixture was then poured into a graphite mold 142 (Grade ATJ, UnionCarbide Co., Carbon Products Div., Cleveland, Ohio), the interior ofwhich measured about 1 inch (25 mm) in diameter by about 21/4 inches (57mm) tall. The graphite mold and its contents were then placed into aroom temperature drying chamber which was contained within a fume hoodand the methylene chloride vehicle was allowed to slowly evaporate fromthe slurry overnight. The following day the graphite mold and itscontents were removed from the drying chamber and placed into a dryingoven at a temperature of about 45° C. After drying at a temperature ofabout 45° C. for about 1 hour, the temperature of the drying oven wasincreased to about 70° C. and the graphite mold and its contents weredried at this temperature for about 2 hours. The drying operationsremoved substantially all of the methylene chloride vehicle. After thedrying operation, the formed sediment cast preform had approximatedimensions of about 1 inch (25 mm) in diameter and about 0.5 inches (13m) thick. The weight of the graphite mold and its contents was about40.75 grams of which 31.75 grams was the mold itself,

The binder was removed from the sediment cast preform by placing thegraphite mold along with the preform contained within into a vacuumfurnace, evacuating the furnace to about 30 inches (762 mm) of mercuryvacuum (pressure less than about 133 Pa) and backfllling the furnacewith argon gas to approximately 2 psig (14 kPag). After repeating theevacuation and backfilling, an argon gas flow rate of about 2 liters perminute at a pressure of about 2 psig (14 kPag) was established andmaintained in the furnace. The furnace temperature was then increasedfrom substantially room temperature to a temperature of about 200° C. ata rate of about 33° C. per hour. Upon reaching a temperature of about200° C., the temperature was then increased to about 350° C. at a rateof about 20° C. per hour. Upon reaching a temperature of about 350° C.,the temperature was then increased to about 600° C. at a rate of about60° C. per hour. Upon reaching a temperature of about 600° C., thetemperature was then decreased to approximately room temperature at arate of about 60° C. per hour. Upon reaching a temperature of about 50°C., the graphite mold 142 and its contents were removed from thefurnace. The weight of the graphite mold and its contents after firingwas about 40.61 grams, about 0.14 grams less than the weight beforefiring. The bulk density of the preform computed to about 1.40 grams percubic centimeter, which converted to about 56 percent of the theoreticaldensity of boron carbide.

About 50.91 grams of zirconium sponge 144 (Nuclear Grade, WesternZirconium Co., Ogden, Utah) was placed on top of the sediment castpreform contained within the graphite mold. The setup comprising thegraphite mold and its contents was then placed into a vacuum furnace atsubstantially room temperature. The furnace was then evacuated toapproximately 30 inches (762 mm) (pressure less than about 133 Pa) ofmercury vacuum and then backfilled with argon gas. The furnace chamberwas evacuated once more to a final pressure of about 3×10⁻⁴ torr (0.040Pa). The furnace temperature was then increased to a temperature ofabout 1000° C. at a rate of about 138° C. per hour. Upon reaching atemperature of about 1000° C., the furnace chamber was backfilled withargon gas and a flow 3% rate of about 2 liters per minute at a pressureof about 2 psig (14 kPag) was established. The remainder of the run wasconducted under this argon atmosphere. The furnace temperature was thenincreased from about 1000° C. to a temperature of about 1900° C. at arate of about 100° C. per hour. After maintaining a temperature of about1900° C. for about 1 hour, the furnace temperature was decreased toabout 1500° C. at a rate of about 50° C. per hour. Upon reaching atemperature of about 1500° C., the furnace cooling was continued down toabout room temperature but at a rate of about 100° C. per hour. Afterthe furnace had cooled to about room temperature, the furnace was openedand the setup was removed from the furnace and disassembled. A plateletreinforced composite comprising zirconium diboride, zirconium carbideand residual metal was recovered. It was observed visually that unlikesome platelet reinforced composites fabricated without additions ofsilicon metal to the preform, that the platelet reinforced composite ofthe present Example did not contain certain bumps and craters on the topsurface thereof, i.e., the surface which previously comprised theinterface between the boron carbide preform and the zirconium parentmetal.

EXAMPLE 13

This Example illustrates that a constituent of the residual metal in theplatelet reinforced composite may be introduced as an additive materialbetween the permeable mass to be reactively infiltrated and the adjacentparent metal. The setup used for fabricating such a composite body isshown schematically in FIG. 12.

A preform 162 was fabricated by sedimentation casting a slurrycomprising boron carbide particulate, isopropyl alcohol and a binderagent. Specifically, about 0.22 grams of XUS 40303.00 ExperimentalBinder (Dow Chemical Co., Midland, Mich.) was added to about 38 grams ofisopropyl alcohol contained within a 1 liter NALGENE® plastic bottle(Nalge Co., Rochester, N.Y.). The plastic bottle and its contents wereplaced into an EBERBACH® shaker (Eberbach Corp., Ann Arbor, Mich.) andshaken for approximately 1 hour to disperse the binder into theisopropyl alcohol solvent. After dispersing the binder into the solvent,the plastic bottle was opened and about 45 grams of 1000 grit TETRABOR®boron carbide particulate (ESK Engineered Ceramics, New Canaan, Conn.)having an average particle size of about 5 microns was added to thebinder solution in the plastic bottle along with about 4 BURUNDUM® ballmilling stones (U.S. Stoneware Corp., Mahwah, N.J.) each measuring about1/2 inch (13 mm) in diameter by about 1/2 inch (13 mm) tall. TheNALGENE® plastic jar was resealed and placed back onto the EBERBACH®shaker and shaken again for approximately 2 hours or until the boroncarbide particulates were thoroughly dispersed and substantially noagglomerates remalned.

The slurry of boron carbide, isopropyl alcohol and binder wasimmediately poured into a Grade ATJ graphite crucible 160 (Union CarbideCo., Carbon Products Division, Cleveland, Ohio) whose interior measuredabout 2 inches (51 mm) square by about 31/4 inches (83 mm) tall. Theslurry was poured into the cruclble at a slight angle to avoid trappingair at the bottom of the pore. The graphite crucible 160 weighed about245.5 grams.

The graphite crucible 160 and the slurry contained within was thenplaced into a fume hood and covered with a layer of construction paperto reduce somewhat the rate of evaporation of solvent from thesedimented slurry of boron carbide and binder. The bulk of the isopropylalcohol solvent evaporated overnight while the crucible 160 and itscontents sat ln the fume hood at room temperature. The graphite crucible160 and the sediment cast preform 162 contained within were then placedinto a drying oven. After drying for approximately 1 hour at atemperature of about 45° C. in air, at atmospheric pressure, thegraphite crucible 160 and its contents were transferred to a drying ovenat a temperature of about 70° C.. After drying at approximately 70° C.for about 2 hours, the graphite crucible 160 and its contents wereremoved from the drying oven and weighed. The sediment cast preformweighed about 40.7 grams and measured about 2 inches (51 mm) square byabout 0.49 inches (12 mm) thick.

The graphite crucible 160 and its contents were then fired at a highertemperature to remove the organic binder from the sediment cast boroncarbide preform 162. Specifically, the graphite crucible 160 and itscontents were placed into a resistance heated controlled atmospherefurnace at room temperature. The furnace chamber was evacuated to about30 inches (762 mm) of mercury vacuum (pressure less than about 133 Pa)and then backfilled with argon gas. An argon gas flow rate of about 2liters per minute through the furnace chamber was established. Thefurnace temperature was then increased to about 200° C. at a rate ofabout 100° C. per hour. Upon reaching a temperature of about 200° C.,the temperature was then increased to about 350° C. at a rate of about20° C. per hour. Upon reaching a temperature of about 350° C., thetemperature was then increased to about 670° C. at a rate of about 64°C. per hour. Upon reaching a temperature of about 670° C., thetemperature was decreased to about room temperature at a rate of about80° C. per hour. Once the furnace had cooled to substantially roomtemperature, the graphite crucible 160 and the sedlment cast boroncarbide preform 162 contained within were removed from the furnacechamber. The weight of the preform 162 was found to be about 40.5 grams.A preform bulk density of about 1.25 grams per cubic centimeter wascalculated which translated to about 49.7 percent of the theoreticaldensity of boron carbide.

About 18.4 grams of niobium particulate 164 (-325 mesh, AtlanticEquipment Engineers Co., Bergenfield, N.J.) having substantially allparticles smaller than about 45 μm was poured into the graphite crucible160 on top of the sediment cast boron carbide preform 162 and leveled.About 228 grams of nuclear grade zirconium sponge 166 (WesternZirconium, Ogden, Utah) was then placed into the graphite crucible 160on top of the layer of niobium particulate 164 to form a lay-up. Thelay-up comprising the graphite cruclble 160 and its contents was thenplaced into a resistance heated controlled atmosphere furnace atsubstantially room temperature. The furnace chamber was evacuated toabout 30 inches (762 mm) of mercury vacuum (pressure less than about 133Pa) and then backfilled with argon gas. The furnace chamber wasevacuated a second time to a final pressure of about 1.8×10⁻⁴ torr(0.024 Pa). The furnace temperature was then increased from about roomtemperature to about 1950° C. at a rate of about 213° C. per hour. Fromroom temperature to about 1000° C. the furnace chamber was heated undervacuum. At a temperature of about 1000° C., the furnace chamber wasbackfilled with argon gas to a pressure of about 2 psig (14 kPag). Anargon gas flow rate of about 2 liters per minute through the furnacechamber was established. During the switch from vacuum to argon gasatmospheres, the furnace heating rate was not interrupted. The remainderof the run was carried out under this argon gas atmosphere. Aftermaintaining a temperature of about 1950° C. for about 2 hours, thetemperature was then decreased to about 1500° C. at a rate of about 90°C. per hour. Upon reaching a temperature of about 1500° C., the rate offurnace cooling was increased such that a temperature substantlallyequal to room temperature was reached in about 4 hours. After thefurnace had cooled to substantially room temperature, the furnace wasopened and the lay-up was removed from the furnace and disassembled. Aplatelet reinforced composite comprising zirconium diboride, zirconiumcarbide and residual metal was recovered.

EXAMPLE 14

This Example demonstrates that a platelet reinforced composite whichincludes an additive material possesses improved resistance tooxidation. Four preforms were fabricated from powder mixtures. Three ofthe preforms included an additive material. The remaining preform didnot include an additive material in order to illustrate the effects ofutilizing an additive material.

The powder mixtures which were utilized to produce the preforms for theformation of oxidation resistant ceramic matrix composite bodies werefabricated on the basis of about 19.5 grams of TETRABOR® 1000 grit(average particle diameter of about 5 μm) boron carbide (ESK EngineeredCeramics, New Canaan, Conn.), about 130 grams of -325 mesh (particlediameter less than about 45 μm) zirconium parent metal powder (TeledyneWah Chang Albany, Albany, Oreg.) and respectfully, one of thefollowing: 1) about 6.4 grams of silicon hexaboride, SiB₆ (ConsolidatedAstronautics, Saddle Brook, N.J.); 2) about 6.5 grams of silicontetraboride, SiB₄ (Atlantic Equipment Engineers, Bergenfield, N.J.); 3)about 8.5 grams of 1000 grit (average particle diameter of about 5 μm)silicon carbide, SiC (Exolon-ESK Corporation, Tonawanda, N.Y), and 4) noadditive powder. Each preform was made by first combining two alumlnamilling balls having a diameter of about 0.5 inch (13 mm), about 30grams of methanol, about 19.5 grams of boron carbide powder, and thespecified amounts of the additive powder into a plastic bottle. Theplastic bottle was closed securing the lid of the plastic bottle. Tapewas wrapped around the perimeter of the lid of the plastic bottle toprevent any leaking. The plastic bottle and its contents were placedonto a reciprocating shaker for about 2 hours. The lid of the plasticbottle was then removed and the plastic bottle and its contents wereplaced into a laboratory hood. After the methanol had substantiallycompletely evaporated from the B₄ C-additive powder mixture, twoadditional alumina milling balls having a diameter of about 0.5 inch (13mm) were placed into the plastic bottle and the plastic bottle wasclosed by resecuring the lid onto the plastic bottle. The plastic bottleand its contents were then placed on a jar mill for about 2 hours tobreak up any agglomerates in the B₄ C-additive powder mixture. Themilled B₄ C-additive powder mixture was then sieved through a 60 mesh(opening of about 250 μm) and about 130 grams of zirconium powder werehand blended into the B₄ C-additive powder mixture to form a preformmixture. Once substantially homogeneously blended, each preform mixturewas placed into a steel die having an inner cavity measuring about 2inches (51 mm) wide and about 2 inches (51 m) long. After the preformmixture was substantially level, a ram was placed in contact with thepreform mixture and the preform mixture was consolidated at a pressureof about 10,000 pounds per square inch (70 MPa). The end of theconsolidation step produced preforms measuring about 2 inches (51 mm)long, about 2 inches (51 mm) wide and about 0.8 inch (20 mm) thick. Thepreforms were placed into graphite boats having Inner cavities measuringabout 2 inches (51 mm) long, about 2 inches (51 mm) wide, about 3.25inches (83 mm) deep and having a wall thickness of about 0.25 inch (6.4mm). The graphite boats were machined from Grade ATJ graphite (UnionCarbide Corporation, Carbon Products Division, Cleveland, Ohio). Ahafnium sponge material was placed onto the surface of each preformcontained within a graphite boat. The hafnium sponge material functionedas an oxygen getter for the processing atmosphere, as discussed below.Several graphite boats containing the preforms comprised of boroncarbide additive powder, zirconium parent metal powder and hafniumgetter material were placed into a graphite tray to form a lay-up.

The lay-up and its contents were placed into a vacuum furnace and thevacuum furnace door was closed. The vacuum furnace chamber wasevacuated, then filled with argon at a flow rate of about 10 liters perminute and evacuated a second time to a pressure of about 1.4×10⁻⁴ torr(0.019 Pa). The vacuum pump was disengaged from the vacuum furnacechamber and argon gas was introduced into the vacuum furnace chamber ata flow rate of about 10 liters per minute until an overpressure of 2pounds per square inch (14 kPa) was attained, then the argon flow ratewas reduced to about 2 liters per minute. The vacuum furnace and itscontents were then heated from about room temperature to about 2000° C.in about 9 hours, held at about 2000° C. for about 2 hours and cooledfrom about 2000° C. to about room temperature in about 8 hours whilemaintaining an argon flow rate of about 2 liters per minute at anoverpressure of about 2 pounds per square inch (0.14 kg/cm²). At aboutroom temperature, the vacuum furnace door was open and the lay-up andits contents were removed to reveal that the preforms had reacted toform ceramic matrix composite bodies containing the additive materialsand one ceramic matrix composite body containing no additive material.

The composite bodies containing no additive material, the composite bodycontaining the silicon carbide (SiC) additive and the composite bodycontaining the silicon hexaboride (SiB₆) additive were cut into couponsmeasuring about 0.4 inch (10 mm) long, 0.4 inch (10 mm) wide and about0.2 inch (5.1 mm) thick. The coupons were placed into an alumina boat toform a lay-up. The lay-up and its contents were then placed into a tubefurnace and the tube furnace and its contents were heated from aboutroom temperature to about 1000° C. at about 200° C. per hour, held at1000° C. for about 24 hours and cooled from about 1000° C. to about roomtemperature at about 200° C. per hour. At about room temperature, thealumina boat and its contents were removed from the tube furnace. AsFIG. 13 reveals, the composite body 170 containing no additive materialhad oxidized, the ceramic composite body 172 containing the siliconcarbide additive had oxidized beyond recognition, while the ceramiccomposite body 174 with the silicon hexaboride additive had maintainedits shape and exhibited a weight gain of only about 1.4 percent. Thus,this Example demonstrates that the addition of silicon hexaboride tocomposite bodies formed by the reactive infiltration of a zirconiumparent metal powder into a permeable mass comprising boron carbide andan additive material may possess improved oxidation resistance.

EXAMPLE 15

This Example demonstrates a method for forming ceramic matrix compositebodies which Incorporate an additive material. A plurality of preformswere fabricated, each of which Included a different additive material.The fabricated preforms were reactively infiltrated with a molten parentmetal.

Table I contains a summary for Sample A through Sample K of the weightpercent boron carbide, weight percent additive, and weight percentparent metal powder used to make preforms for the formation of ceramicmatrix composite bodies. Further, Table I Includes the density of theresultant ceramic matrix composite bodies.

                                      TABLE I                                     __________________________________________________________________________                         Weight Percent                                               Weight Percent                                                                        Weight Percent                                                                         -325 Mesh Zr                                                                             Density Ceramic                               Sample                                                                            1000 grit B.sub.4 C                                                                   Additive Material                                                                      Percent Metal Powder                                                                     Composite                                     __________________________________________________________________________    A   12.2    6.6                                                                              (Al.sub.2 O.sub.3)                                                                  81.2       5.46                                          B   11.8    9.5                                                                              (ZrO.sub.2)                                                                         78.7       5.65                                          C   11.6    11.3                                                                             (CeO.sub.2)                                                                         77.1       5.60                                          D   12.0    8.2                                                                              (Y.sub.2 O.sub.3)                                                                   79.8       5.92                                          E   11.7    10.4                                                                             (La.sub.2 O.sub.3)                                                                  77.9       5.89                                          F   12.3    6.0                                                                              (MgAl.sub.2 O.sub.4)                                                                81.7       5.24                                          G   12.3    5.4                                                                              (SiC) 82.3       5.71                                          H   11.0    15.4                                                                             (HfO.sub.2)                                                                         73.6       5.80                                          I   12.2    6.6                                                                              (Al.sub.2 O.sub.3)                                                                  81.2       5.42                                          J   11.8    9.2                                                                              (ZrO.sub.2)                                                                         79.0       5.98                                          K   13.0    0        87.0       6.11                                          __________________________________________________________________________

Powder mixtures used to produce preforms corresponding to Samples Athrough Sample K of Table I were made on the basis of about 19.5 gramsof TETRABOR® 1000 grit (average particle diameter of about 5 μm) boroncarbide (ESK Engineered Ceramics, New Canaan, Conn.), about 130 grams of-325 mesh (particle diameter less than about 45 μm) zirconium parentmetal powder (Teledyne Wah Chang Albany, Albany, Oreg.) and one of eachof the following different additives: (A) regular ground alumina (AlcanChemical, Cleveland, Ohio), Grade TZ-3Y (average particle diameter ofabout 0.3 lm); (B) zirconia (Tosoh USA, Atlantic, Ga.); (C) cerium oxide(Atlantic Equipment Engineers, Bergenfield, N.J.); (D) yttrium oxide(MolyCorp, Inc., a Unocal Company, White Plains, N.Y.); (E) lanthanumoxide (MolyCorp, Inc., a Unocal Company, White Plains, N.Y.); (F) -325mesh (particle diameter less than about 45 μm) magnesium aluminatespinel (Atlantic Equipment Engineers, Bergenfield, N.J.); (G) 1000 grit(average particle diameter of about 5 μm) silicon carbide (ESKEngineered Ceramic, New Canaan, Conn.); (H) hafnium oxide (ConsolidatedAstronautics, Saddle Brook, N.J.); (I) Grade T-64 alumina (Alcoa,Pittsburgh, Pa.); (J) Grade MS2 (average particle diameter less thanabout 2 μm) zirconia (Magnesium Electron, Inc., Flemington, N.J.) and(K) which did not include an additive material. Each preform was made byfirst combining two alumina milling balls each having a diameter ofabout 0.5 inch (13 mm), about 30 grams of methanol, about 19.5 grams ofboron carbide powder, and the specified amount of one additive, as shownin Table I, in a plastic bottle. The plastic bottle was closed bysecuring the lid of the plastic bottle. Tape is was wrapped around theperimeter of the lid of the plastic bottle to prevent leaking. Theplastic bottle and its contents were placed onto a reciprocating shakerfor about 2 hours. The lid of the plastic bottle was then removed andthe plastic bottle and its contents were placed into a laboratory hood.After the methanol had substantially completely evaporated from the B₄C-additive mixture, two additional alumina milling balls were placedinto the plastic bottle and the lid of the plastic bottle was closed byresecuring the lid onto the bottle. The plastic bottle and its contentswere then placed on a jar mill for about 2 hours to break up anyagglomerates in the B₄ C-additive mixture. The milled B₄ C-additivemixture was then sieved through a 60 mesh (opening of about 250 μm)screen. About 130 grams of zirconium powder were hand blended into theseived B₄ C-additive mixtures to form preform mixtures. Oncesubstantially homogeneously blended, the preform mixtures were placed,one at a time, into a steel die having an inner cavity measuring about 2inches (51 mm) wide and about 2 inches (51 mm) long. After the preformmixture was substantially leveled, a ram was placed in contact with theleveled preform mixture within the steel die and the preform mixture wasconsolidated with a pressure of about 10,000 lbs per square inch (70MPa). The consolidation step produced preforms measuring about 2 inches(51 mm) long, about 2 inches (51 mm) wide and about 0.8 inch (20 mm)thick. The preforms were then placed into graphite boats having innercavities, measuring about 2 inches (51 mm) long, about 2 inches (51 mm)wide, about 3.25 inches (83 mm) deep and having a wall thickness ofabout 0.25 inches (6.4 mm). The graphite boats were machined from GradeATJ graphite (Union Carbide Corporation, Carbon Products Division,Cleveland, Ohio). A hafnium sponge material was placed onto the surfaceof each preform contained within the respective graphite boats. Thehafnium sponge material functioned as a oxygen getter for the processingatmosphere as discussed below. The graphite boats and their contentswere placed into a graphite tray to form a lay-up.

The lay-up and its contents were placed into a vacuum furnace, and thevacuum furnace door was closed. The vacuum furnace chamber wasevacuated, filled with argon at a flow rate of at least 10 llters perminute and evacuated a second time to a pressure of about 1.4×10⁻⁴ torr(0.019 Pa). The vacuum pump was disengaged from the vacuum furnace ischamber and argon gas was introduced into the vacuum furnace chamber ata flow rate of about 10 liters per minute until an overpressure of about2 pounds per square inch (14 kPa) was attained, then the argon flow ratewas reduced to about 2 liters per minute. The vacuum furnace and itscontents were then heated from about room temperature to about 2000° C.in about 9 hours, held at 2000° C. for about 2 hours and cooled fromabout 2000° C. to about room temperature in about 8 hours whilemaintaining in argon flow rate of about 2 liters per minute at anoverpressure of about 2 pounds per square inch (14 kPa). At about roomtemperature, the furnace was opened and the lay-up and its contents wereremoved to reveal that the parent metal powder and the boron carblde hadreacted to form ceramic matrix composite bodies incorporating anadditive material. The previously-identified Table I also contains asummary of the densities of a resultant ceramic matrix composite bodieswhich as measured by a method that was substantially similar to ASTMC373-56 Standard Method of Test for Water Absorption Bulk Density,Apparent Porosity Apparent Specific Gravity of Fired Porous WhitewareProducts.

EXAMPLE 16

The following Example demonstrates a method for the formation of ceramicmatrix composite bodies incorporating a variety of additives by themethod of the present invention.

Eight preforms were prepared, which each comprised TETRABOR® 1000 grit(average particle diameter of about 5 μm, ESK Engineered Ceramics, NewCanaan, Conn.) boron carbide and a different additive material selectedfrom following additive compositions: (1) -325 mesh (particle diameterless than 45 μm) magnesium oxide, (2) alumina (Alcan Corporation,Montreal, Canada), (3) yttrium oxide (Rhone-Pulenc, Inc., ChemicalsDivision, Princeton, N.J.), (4) Grade TZ-3Y (average particle diameterof about 0.3 μm) zirconia (Tosoh USA, Atlanta, Ga.), (5) zirconia(Magnesium Elektron, Inc., Flemington, N.J.), (6) cerium oxide, (7) -200mesh (particle diameter less than about 75 μm) magnesium aluminatespinal (Atlantic Equipment Engineers, Bergenfield, N.J.), and (8)ytterbium oxide (MolyCorp, Inc., a Unocal Company, White Plains, N.Y.).Each preform was prepared by first placing about 45 grams of the 1000grit (average particle diameter of about 5 μm) baron carbide into aplastic bottle, along with an amount of one of the above-listedadditives equal to about 10 volume percent of the boron carbide. The lidto the plastic bottle was secured, and the plastic bottle and itscontents were hand shaken in order to mix the boron carbide and theadditive to form a substantially homogeneous B₄ C-additive mixture. TheB₄ C-additive mixture was then poured into the bottom of a graphite boat(Grade ATJ graphite, Union Carbide Corporation, Carbon ProductsDivision, Cleveland, Ohio) having an inner cavity measuring about 2inches (51 mm) long, by about 2 inches (51 mm) wide, by about 3.25inches (83 mm) deep, and having a wall thickness of about 0.25 inch (6.4mm). The B₄ C-additive mixture was leveled, and the graphite boat andits contents were placed on a tap density meter (Model 2003Stampfvolumeter, J. Engelsmann AG, West Germany) in order to tap loadthe B₄ C-additive mixture within the graphite boat. The graphite boatand its contents were tapped about 500 times in order to consolidate theB₄ C-additive mixture to form a preform. About 610 grams of nucleargrade -1/4 mesh+20 mesh (particle diameter from about 0.85 mm to about6.3 mm) zirconium metal sponge were then poured onto the preform withinthe graphite boat.

The eight graphite boats and their contents were placed onto a graphitetray to form a lay-up. The lay-up and its contents were placed into avacuum furnace, and the vacuum furnace door was closed. The vacuumfurnace chamber was evacuated to about 2×10⁻⁴ torr (0.027 Pa) and filledwith argon at a rate of about 10 liters per minute until an overpressureof about 2 pounds per square inch (14 kPa) was obtained, then the argonflow rate was reduced to about 2 liters per minute. The vacuum furnaceand its contents were then heated from about room temperature to about2000° C. in about 8 hours, held at about 2000° C. for about 2 hours, andcooled from about 2000° C. to about room temperature in about 8 hourswhile maintaining the argon flow rate at about 2 liters per minute andan overpressure of about 2 pounds per square inch (14 kPa). At aboutroom temperature, the argon flow rate was interrupted and the vacuumfurnace door was opened to reveal that the zirconium metal hadreactively infiltrated the preforms comprised of the B₄ C-additivemixtures.

The resultant ceramic composite bodies were cross sectioned, mounted andpolished for metallographic examination by a scanning electronmicroscope set in the back scattered electron mode. Specifically, FIG.14 is a photomicrograph taken at about 1000× corresponding to theceramic matrix composite body incorporating the -325 mesh (particledlameter less than about 45 μm) magnesium oxide additive. FIG. 15 is aphotomicrograph taken at about 1000× corresponding to the ceramic matrixcomposite body incorporating the alumina additive. FIG. 16 is aphotomicrograph taken at about 1000× corresponding to the ceramic matrixcomposite body incorporating the yttrium oxide additive. FIG. 17 is aphotomicrograph taken at about 1000× corresponding to the ceramic matrixcomposite body incorporating the Grade TZ-3Y zirconia additive. FIG. 18is a photomicrograph taken at about 1000× corresponding to the ceramicmatrix composite body incorporating the zirconia (Magnesium Elektron,Inc.) additive. FIG. 19 is a photomicrograph taken at about 1000×corresponding to the ceramic matrix composite body incorporating thecerium oxide additive. FIG. 20 is a photomicrograph taken at about 1000×corresponding to the ceramic matrix composite body incorporating themagnesium aluminate spinel additive. FIG. 21 is a photomicrograph takenat about 1000× corresponding to the ceramic matrix composite bodyincorporating the ytterbium oxide additive.

EXAMPLE 17

This Example illustrates utilizing an additive material which wasapplied to the interface between the pemeable mass comprising boroncarbide and the parent metal. Specifically, this Example was utilized tofabricate a platelet reinforced composite extrusion die. The setup whichwas employed in carrylng out the fabrication of this extrusion die isillustrated schematically in FIG. 22.

The graphite containment means for the boron carbide material, theinterfacial additive material, and the parent metal was assembled.Speciflcally, a Grade ATG graphlte crucible 180 (Union CarbideCorporation, Carbon Products Division, Cleveland, Ohio) measuring in itsinterior about 2.0 inches (51 mm) In diameter by about 3.25 inches (83mm) tall was increased in total height by about 1.0 inch (25 mm) bygluing a is graphite tube 182 to the top of the crucible. The inside andoutside diameters of the graphite extension tube 182 were substantiallythe same as those of the graphite crucible 180. The banding meanscomprised a layer of GRAPHI-BOND® colloidal graphite cement 184 (AremcoProducts Inc., Ossining, N.Y.). The bonded graphite pieces were thenplaced into a drying oven at a temperature of about 120° C. After aboutthree hours at a temperature of about 120° C., the graphite cement hadsubstantially cured to completion and the bonded graphite bodies 162,180 were removed from the drying oven.

The inner surface of the platelet reinforced composite extrusion die tobe formed was defined and bounded by a Grade ATJ graphite mandrel 186(Union Carbide Corp., Carbon Products Divisions Cleveland, Ohio). Thisgraphite mandrel 186 was fixed in place by bonding to the center of thebase of the graphite containment means or cruclble located above. A band188 between the mandrel and the crucible was achloved using GRAPHI-BOND®cement by substantially the same technique as described previously.

About 39 grams of 1000 grit TETRABOR® boron carbide particulate 190(ESK-Engineered Ceramics, New Caanan, Conn.) having an average particlesize of about 5 μm was poured into the cavity between the walls of thegraphite crucible 180 and the graphite mandrel 186 and levelled. Thegraphite crucible 180 and its contents were then placed into a Model2003 STAV tap volume meter (Stampfvolumeter, J. Engellmann, A. G.Federal Republic of Germany) and tap loaded about 500 times to compactthe loose baron carbide particulate into a semi-rigid preform and tominimize as much entrapped air as possible. About 7.26 grams of nioblumparticulate 192 (-325 mesh, Atlantic Equipment Engineers, Bergenfield,,N.J.), having substantially all particles smaller than about 45 μm indiameter was sprinkled substantially evenly over the tap loaded layer ofboron carbide particulate 190 in the graphite crucible 180. About 290.53grams of nuclear grade zirconium sponge 194 (Western Zirconium, Ogden,Utah) was then placed into the graphite crucible 180 on top of thelevelled layer of niobium particulate 192 to form a lay-up 196.

The lay-up 196 comprising the graphite crucible and its contents wasthen placed into a vacuum furnace at about room temperature. The vacuumchamber was evacuated to about 30 inches (762 mm) of mercury vacuum(pressure less than about 133 Pa) using a mechanical roughing pump andthen back-filled with argon gas. After repeating this evacuation andback-filling procedure, the vacuum chamber was evacuated once more toabout 30 lnches (762 mm) of mercury vacuum (pressure less than about 133Pa). A high vacuum source was then connected to the vacuum chamber andthe chamber was evacuated to a final working pressure of about 2×10⁻⁴torr (0.027 Pa). The furnace temperature was then increased from aboutroom temperature to a temperature of about 1950° C. at a rate of about192° C. per hour. Upon reaching a temperature of about 1000° C., thevacuum chamber was back-filled with argon gas. An argon gas flow rate ofabout two liters per minute at a pressure of about 2 psig (14 kPa) wasastablishad through the vacuum chamber. The remainder of the furnace runwas executed under this argon atmosphere. After maintaining atemperature of about 1950° C. for about two hours, the furnacetemperature was then decreased to about 1400° C. at a rate of about 92°C. per hour. Upon reaching a temperature of about 1400° C., the furnacetemperature was further decreased to about room temperature at a rate ofabout 274° C. per hour. The lay-up 196 was removed from the furnace atabout room temperature. The lay-up 196 was disassembled to reveal that aplatelet reinforced composite body had formed. The formed body hadsubstantially the net-shape of the desired extrusion die. Specifically,the outside diameter of the formed body was defined by the insidediameter of the graphite-crucible 180 and the inner-surface of theformed body conformed to the outer-surface of the graphite mandrel 186.The formed platelet reinforced composite extrusion die was sectionedvertically using electro-discharge machining (EDM). FIGS. 23a, 23b and23c show top, bottom, and cross-sectional views, respectively, of theformed extrusion die. Some excess platelet reinforced composite materialwas mounted in plastic, polished using diamond paste, and examined in anoptical microscope. Quantitative image analysis of the fields examinedby the optical microscope revealed that the formed platelet reinforcedcomposite comprised about 16 volume percent residual metal and thebalance zirconium diboride and zirconium carbide.

EXAMPLE 18

The following Example further demonstrates a method for the formation ofceramic matrix composite bodies incorporating a variety of additives bythe method of the present invention.

Five preforms were prepared, each preform comprising TETRABOR® 1000 grit(average particle diameter of about 5 μm), boron carbide (ESK EngineeredCeramics, New Canaan, Conn.) and having a different additive materialselected from the following additive compositions: 1) -325 mesh(particle diameter less than about 45 μm) zirconium oxide, 99.9% pure(Atlantic Equipment Engineers, Bergenfield, N.J.); 2) Grade TZ-3Yyttrlum oxide stabilized zirconia (average particle size about 0.3 μm)(Tosoh USA, Atlanta, Ga.); 3) zircon powder (Excelopax, Tam Ceramics,Niagara Falls, N.Y.); 4) -325 mesh (particle diameter less than about 45μm) hafnium oxide, 99.95% pure (Consolidated Astronautics, Saddle Brook,N.J.); and 5) yttrium oxide (Research Chemicals, Nucor Corporation,Phoenix, Ariz.). Each preform was prepared by first placing about 40.5grams of the 1000 grit boron carbide into a plastic bottle, along withan amount of each one of the above listed additives equal to about 10volume percent of the boron carbide. The lid to the plastic bottle wassecured, and the plastic bottle and its contents were placed onto anorbital mixer to form a substantially homogeneous boron carbide-additivemixture. After about 2 hours, the plastic bottle and its contents wereremoved from the orbital mixer.

A graphite boat (Grade ATJ graphite, Union Carbide Corporation, CarbonProducts Division, Cleveland, Ohio) having an internal cavity measuringabout 2 inches (51 mm) square by about 3.25 inches (83 mm) deep wasprepared by cleaning the surfaces with ethyl alcohol. A temperature ofabout 100° C. was established within a drying oven and the graphite boatwas placed within the drying oven. When the graphite boat wassubstantially completely dry, it was removed from the oven and the boroncarbide-additlve mixture was poured into the bottom of the graphiteboat. The boron carbide-additive mixture was leveled, and the graphiteboat and niobium partlculato 192 to form a lay-up 196. its contents wereplaced on a tap density meter (Model 2003 Stampfvolumeter, J. EnglesmannAG, West Germany) in order to tap load the boron carbide-additivemixture within the graphite boat. The graphite boats containing thefirst four mixtures were tapped about 500 times in order to consolidatethe boron carbide-additive mixture to form a preform. The graphite boatcontaining the fifth mixture was tapped about 300 times in order toconsolidate the boron carbide-additive mixture to form a preform. About322 grams of -1/4 mash+20 mesh (particle diameter from about 0.85 mm toabout 6.3 mm) nuclear grade zirconium metal sponge (Western ZirconiumCompany, Ogden, Utah) were then carefully poured onto the preform withinthe graphite boat. A temperature of about 40° C. was established withina drying oven. The five graphite boats and their contents were placedinto the drying oven overnight.

The five graphite boats and their contents were removed from the dryingoven and were placed onto a graphite tray to form a lay-up. The lay-upand its contents were placed into a vacuum furnace, and the vacuumfurnace door was-closed. The vacuum furnace chamber was evacuated toabout 2×10⁻⁴ torr (0.027 Pa) and backfilled with argon gas at a rate ofabout 2 liters per minute until an overpressure of about 2 pounds persquare inch (14 kPa) was obtained. An argon gas flow rate of about 2liters per minute was maintained, and the vacuum furnace and itscontents were heated from about room temperature to about 2000° C. inabout 4 hours. After maintaining a temperature of about 2000° C. forabout 2 hours, the furnace temperature was decreased to about roomtemperature in about 3.5 hours. At about room temperature, the argon gasflow was interrupted and the vacuum furnace door was opened to revealthat the zirconium metal had reactively infiltrated the preformscomprised of the boron carbide-additive mixtures.

The resultant ceramic composite bodies were cross sectioned, mounted andpolished for metallographic examination by a scanning electronmicroscope set in the backscattered electron mode. Specifically, FIG. 24is a photomicrograph taken at about 1000× corresponding to the ceramicmatrix composite body incorporating the zirconium oxide additive. FIG.25 is a photomicrograph taken at about 1000× corresponding to theceramic matrix composite body incorporating the Grade TZ-3Y yttriumoxide stabilized zirconium oxide additive. FIG. 26 is a photomicrographtaken at about 1000× corresponding to the ceramic matrix composite bodyincorporating the zircon powder additive. FIG. 27 is a photomicrographtaken at about 1000× corresponding to the ceramic matrix composite bodyincorporating the -325 mesh hafnium oxide additive. FIG. 28 is aphotomicrograph taken at about 1000× corresponding to the ceramic matrixcomposite body incorporating the yttrium oxide additive.

While the present invention has been disclosed in its preferredembodiments, it is to be understood that the invention is not limited tothe precise disclosure contained herein, but may otherwise be embodiedin various changes, modifications, and improvements which may occur tothose skilled in the art, without departing from the scope of theinvention, as defined in the appended claims.

We claim:
 1. A method of producing a self-supporting body comprising:selecting a parent metal; providing a permeable mass comprising at least one property-modifying additive comprising at least one metallic material selected from the group consisting of Nb, Ti, W, Mo, V, Hf, Ta, Cr, Al, Si, Ni and Co, and at least one material selected from the group consisting of (1) boron carbide, (2) a boron source material and a carbon source material and (3) boron carbide and at least one of a boron source material and a carbon source material; heating said parent metal in a substantially inert atmosphere to a temperature above its melting point to form a body of molten parent metal and contacting said body of molten parent metal with said permeable mass; maintaining said temperature for a time sufficient to permit infiltration of said molten parent metal into said permeable mass and to permit reaction of said molten parent metal with said permeable mass; and continuing said infiltration reaction for a time sufficient to produce said self-supporting body, whereby said at least one additive modifies at least one property in said self-supporting body.
 2. The method of claim 1 further comprising adding to said metallic material at least one material from the group consisting of VC, NbC, WC, W₂ B₅, and Mo₂ B₅.
 3. The method of claim 1, wherein said parent metal comprises at least one metal selected from the group consisting of titanium, zirconium and hafnium.
 4. The method of claim 1, wherein said substantially inert atmosphere comprises an argon atmosphere.
 5. The method of cliam 1, wherein at least one second additive is provided to said permeable mass, said at least one second additive comprising at least one material selected from the group consisting of Al₂ O₃, MgO, MgAl₂ O₄, Y₂ O₃, La₂ O₃, CaO, HfO₂, SiB₄, SiB₆, ZrSiO₄, Yb₂ O₃ and ZrO₂.
 6. The method of claim 3, further comprising providing at least one second additive, wherein said at least one second additive comprises at least one material selected from the group consisting of CeO₂, TaC, ZrC, SiC, VC, NbC, ZrB₂, TaB₂, W₂ B₅ and Mo₂ B₅.
 7. A method of producing a self-supporting body comprising:selecting a parent metal; providing a permeable mass comprising at least one material selected from the group consisting of (1) boron carbide; (2) a boron source material and a carbon source material and (3) boron carbide and at least one of a boron source material and a carbon source material; providing at least one property-modifying additive by application to a least a portion of an interface between said parent metal and said permeable mass; heating said parent metal in a substantially inert atmosphere to a temperature above its melting point to form a body of molten parent metal and contacting said body of molten parent metal with said permeable mass; maintaining said temperature for a time sufficient to permit infiltration of said molten parent metal into said permeable mass and to permit reaction of said molten parent metal with said permeable mass; and continuing sid infiltration reaction for a time sufficient to produce said self-supporting body, whereby said at least one additive modifies at least one property in said self-supporting body.
 8. The method of claim 7, werein said parent metal comprises at least one material selected from the group consisting of titanium, zirconium and hafnium.
 9. The method of claim 7, werein said substantially inert atmosphere comprises an argon atmosphere.
 10. A method of producing a self-supporting body comprising:selecting a parent metal; providing a permeable mass comprising at least one material selected from the group consisting of (1) boron carbide, (2) a boron source material and a carbon source material and (3) boron carbide and at least one of a boron source material and a carbon source material; providing at least one property-modifying additive comprising niobium; heating said parent metal in a substantially inert atmosphere to a temperature above its melting point to form a body of molten parent metal and contacting said body of molten parent metal with said permeable mass; maintaining said temperature for a time sufficient to permit infiltration of said molten parent metal into said permeable mass and to permit reaction of said molten parent metal with said permeable mass; and continuing said infiltration reaction for a time sufficient to produce said self-supporting body, whereby said at least one additive modifies at least one property in said self-supporting body.
 11. The method of claim 10, wherein said parent metal comprises at least one metal selected from the group consisting of titanium, zirconium and hafnium.
 12. The method of claim 10, wherein said substantially inert atmosphere comprises an argon atmosphere.
 13. The method of claim 10, wherein said niobium is present in an amount of about 0.5 to about 10 percent by weight.
 14. The method of claim 13, wherein said niobium is present in an amount of about 1 to about 5 percent by weight.
 15. A self-supporting body made according to claim
 1. 